# Thread Handoff - Thread: golden-harbor-9953 - UUID: ba7d0545-fc9a-490c-b9f6-581bd7a59479 - CTF: midnight-sun-ctf-2026-quals - Challenge: empols - Runtime: codex - Model: gpt-5.5 - Status: completed ## Transcript - **Assistant:** I’ll inspect the local challenge files first, then connect to the service once I know what protocol or binary we’re dealing with. I’ll keep notes of concrete findings as I go. - **Assistant:** There’s only a tiny local hint file, so the real challenge is the remote TCP service. I’m reading that hint now, then I’ll probe the server interaction. - **Assistant:** The service is menu-driven and reachable. It shows options for Help and Play, so I’m going through the help text before attempting automation. - **Assistant:** The help text says the task is to automatically generate validating strings for 20 gzipped binaries. I’m starting a fresh Play session to see the exact transport format and validation prompt. - **Assistant:** Play mode appears to switch into a binary transfer or non-printing protocol after the initial line, so I’m switching from interactive `nc` to a small socket probe that prints escaped bytes. That should reveal where the gzip payload begins and how answers are expected. - **Assistant:** b' \x1b[38;5;51m\xe2\x96\x84\x1b[48;5;87m\xe2\x96\x84\x1b[0m\x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\x1b[48;5;87m\xe2\x96\x84\x1b[0m\x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84 \xe2\x96\x84\x1b[38;5;51m\x1b[48;5;87m\xe2\x96\x84\x1b[0m\x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\x1b[48;5;87m\xe2\x96\x84\x1b[0m\x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84\x1b[0m \x1b[38;5;51m\xe2\x96\x84\x1b[48;5;87m\xe2\x96\x84\x1b[0m\x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84\x1b[0m \x1b[38;5;51m\x1b[48;5;87m\xe2\x96\x84\x1b[0m\x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x84\x1b[48;5;87m\xe2\x96\x84\x1b[0m\x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m\n \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[48;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[48;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[48;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\x1b[48;5;44m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m\n \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[48;5;44m\xe2\x96\x80\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x80\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88 \xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m\x1b[38;5;51m\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\x1b[0m \n \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[48;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88 \x1b[0m\x1b[38;5;44m\xe2\x96\x80\x1b[38;5;51m\x1b[48;5;44m\xe2\x96\x80\x1b[0m\x1b[38;5;44m\xe2\x96\x80\x1b[0m\x1b[38;5;51m \xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[48;5;44m\xe2\x96\x80\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88 \xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;44m\xe2\x96\x80\x1b[0m\x1b[38;5;51m\x1b[48;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m\n \x1b[38;5;51m\xe2\x96\x88\xe2\x96' 4822 b'\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88 \xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m\x1b[38;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\x1b[0m \x1b[38;5;51m\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x84\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m\n \x1b[38;5;51m\x1b[48;5;44m\xe2\x96\x80\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88 \xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\x1b[48;5;44m\xe2\x96\x80\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x80\x1b[0m \x1b[38;5;51m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\x1b[0m \x1b[38;5;51m\x1b[48;5;44m\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x88\xe2\x96\x80\x1b[0m\n \x1b[38;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \x1b[38;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80 \xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \x1b[38;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \x1b[38;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \x1b[38;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \x1b[38;5;44m\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\xe2\x96\x80\x1b[0m \n \n> \x1b[1mChoose:\x1b[0m\n\n 1) Help\n 2) Play\n\nSolve twenty random gzipped binaries...\n' b'\x88\xe2\x96\x88' - **Assistant:** chunk 41 b'\nSolve twenty random gzipped binaries...' chunk 1 b' ' total 42 b'\nSolve twenty random gzipped binaries...\n ' gzip idx -1 - **Assistant:** The service prints “Solve twenty random gzipped binaries...” and then stalls with no visible delimiter or gzip magic in a raw socket read. I’m checking whether it is just slow generation or whether it expects an answer immediately after a hidden prompt. - **Assistant:** at 0.3 chunk 41 b'\nSolve twenty random gzipped binaries...\n' at 0.3 chunk 1 b' ' closed total 42 gzip -1 tail b'\nSolve twenty random gzipped binaries...\n ' - **Assistant:** b'\nSolve twenty random gzipped binaries...\n ' - **Assistant:** The payload is hex-encoded gzip, followed by `ANSWER:`. Next I’m going to decode one binary, inspect what kind of executable it is, and derive a repeatable solver for all 20 rounds. - **Assistant:** match True hexlen 4162 blob 14472 7f454c46020101000000000000000000 - **Assistant:** I decoded the first payload successfully: it is a small ELF executable. I’m checking its imports and disassembly now to identify the input-checking pattern. - **Assistant:** It's over Johnny! - **Assistant:** The checker is a stripped x86-64 PIE that copies `argv[1]`, builds the expected string from `.rodata`, and compares with `strcmp`. For the sample, the expected value is just the long alphanumeric string embedded in the binary, so the remote solver can decode gzip, extract that string, send it, and repeat. - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 71, in main() File "/workspace/solve_empols.py", line 52, in main answer = answer_from_elf(elf) ^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 30, in answer_from_elf raise ValueError("no answer-like string found") ValueError: no answer-like string found - **Assistant:** The first automated attempt failed because not every generated answer is strictly alphanumeric. I’m tightening extraction to follow the actual `memcpy` source address in the machine code instead of guessing from character class. - **Assistant:** Traceback (most recent call last): File "/workspace/solve_empols.py", line 116, in main() File "/workspace/solve_empols.py", line 80, in main sock = socket.create_connection((HOST, PORT), timeout=10) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/socket.py", line 865, in create_connection raise exceptions[0] File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/socket.py", line 850, in create_connection sock.connect(sa) ConnectionRefusedError: [Errno 111] Connection refused - **Assistant:** The extractor is now instruction-driven, but the last connection attempt got `ConnectionRefusedError`, likely a transient service restart or rate limit. I’ll retry after a short pause and keep the solver unchanged unless the service response indicates another bug. - **Assistant:** menu received (2407 bytes) 01: b'1ExppiGo4nB5jFBSjuztSuOKMnfMCJoRIJJRklkYEEG5jAh5myg67XyZw65O48cEUk3LkzID8u0Dzq2uDKhfd' Traceback (most recent call last): File "/workspace/solve_empols.py", line 116, in main() File "/workspace/solve_empols.py", line 89, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 17, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** The service closed after round 1 even though the extracted embedded string looked plausible. I’m going to save the current round binary during solving and locally verify whether that string actually triggers the success return before submitting it. - **Assistant:** < 2026/05/10 14:15:55.515137 length=18 from=6538 to=6555 49 74 27 73 20 6f 76 65 72 20 4a 6f 68 6e 6e 79 It's over Johnny 21 0a !. -- It's over Johnny! - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 118, in main() File "/workspace/solve_empols.py", line 99, in main answer = answer_from_elf(elf) ^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 76, in answer_from_elf raise ValueError("no memcpy answer source found") ValueError: no memcpy answer source found - **Assistant:** The binaries are not all the same template. I hit an XOR-checking variant: it loops over 10 input bytes and checks `(input[i] ^ 0xd8) == encoded[i]`, so the answer is `encoded[i] ^ 0xd8`. I’m collecting a few first-round samples to cover the generator templates before rerunning the full 20-round solver. - **Assistant:** Traceback (most recent call last): File "", line 1, in File "/opt/ctf-venv/lib/python3.12/site-packages/angr/__init__.py", line 39, in from .sim_procedure import SimProcedure File "/opt/ctf-venv/lib/python3.12/site-packages/angr/sim_procedure.py", line 9, in from cle import SymbolType File "/opt/ctf-venv/lib/python3.12/site-packages/cle/__init__.py", line 13, in from .backends import ( File "/opt/ctf-venv/lib/python3.12/site-packages/cle/backends/__init__.py", line 3, in from .backend import ALL_BACKENDS, Backend, ExceptionHandling, FunctionHint, FunctionHintSource, register_backend File "/opt/ctf-venv/lib/python3.12/site-packages/cle/backends/backend.py", line 9, in import archinfo File "/opt/ctf-venv/lib/python3.12/site-packages/archinfo/__init__.py", line 10, in from .arch import ( File "/opt/ctf-venv/lib/python3.12/site-packages/archinfo/arch.py", line 22, in import pyvex as _pyvex File "/opt/ctf-venv/lib/python3.12/site-packages/pyvex/__init__.py", line 8, in from . import const, expr, stmt File "/opt/ctf-venv/lib/python3.12/site-packages/pyvex/const.py", line 5, in from .enums import VEXObject, get_enum_from_int File "/opt/ctf-venv/lib/python3.12/site-packages/pyvex/enums.py", line 3, in from .native import ffi, pvc File "/opt/ctf-venv/lib/python3.12/site-packages/pyvex/native.py", line 63, in pvc: Any = _find_c_lib() # This should be properly typed, but this seems non trivial ^^^^^^^^^^^^^ File "/opt/ctf-venv/lib/python3.12/site-packages/pyvex/native.py", line 52, in _find_c_lib _parse_ffi_str() File "/opt/ctf-venv/lib/python3.12/site-packages/pyvex/native.py", line 19, in _parse_ffi_str cache_location = os.path.join(tempfile.gettempdir(), f"pyvex_ffi_parser_cache.{getpass.getuser()}.{hash_}") ^^^^^^^^^^^^^^^^^^^^^ File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/tempfile.py", line 315, in gettempdir return _os.fsdecode(_gettempdir()) ^^^^^^^^^^^^^ File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/tempfile.py", line 308, in _gettempdir tempdir = _get_default_tempdir() ^^^^^^^^^^^^^^^^^^^^^^ File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/tempfile.py", line 223, in _get_default_tempdir raise FileNotFoundError(_errno.ENOENT, FileNotFoundError: [Errno 2] No usable temporary directory found in ['/tmp', '/var/tmp', '/usr/tmp', '/workspace'] - **Assistant:** Traceback (most recent call last): File "/workspace/capture_one.py", line 5, in s = socket.create_connection(("empols.play.ctf.se", 3337), timeout=10) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/socket.py", line 865, in create_connection raise exceptions[0] File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/socket.py", line 850, in create_connection sock.connect(sa) ConnectionRefusedError: [Errno 111] Connection refused - **Assistant:** The static solver now handles the two observed checker families and locally verifies candidates by running each decoded ELF before sending. I’ve confirmed both saved samples return the success code with the derived answers. - **User:** The binary format may not consistent. To get each binary's flag, you'd better to utilize `angr` or simillar SMT-solver tools for a better approach for each steps' binary given via base64. - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 156, in main() File "/workspace/solve_empols.py", line 135, in main answer = answer_from_elf(elf) ^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 82, in answer_from_elf raise ValueError("no memcpy answer source found") ValueError: no memcpy answer source found - **Assistant:** Agreed that the format/checker template varies. The service is actually sending hex-encoded gzip rather than base64 in my sessions; I’m currently using static extraction plus local execution as a guard, and I’ll fall back to SMT if a new template fails local validation. - **Assistant:** A third template appeared, so the static solver is not complete. I’m inspecting the saved round binary and then I’ll switch to a per-binary constraint solver path rather than chasing every template manually. - **Assistant:** This third template is a word-sum checker: it treats the input as big-endian 16-bit pairs and requires `pair + table_a[i] == table_b[i]`. I’m adding a generic parser for those stack-initialized word tables, then local validation will confirm the candidate before any remote submission. - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 198, in main() File "/workspace/solve_empols.py", line 166, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 19, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** The expanded solver locally validates the word-sum sample. The last remote session closed before sending the first `ANSWER:` marker, which looks like the service refusing/aborting a session rather than a solver error; I’m retrying with the same code. - **Assistant:** Traceback (most recent call last): File "/workspace/solve_empols.py", line 198, in main() File "/workspace/solve_empols.py", line 157, in main sock = socket.create_connection((HOST, PORT), timeout=10) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/socket.py", line 865, in create_connection raise exceptions[0] File "/root/.local/share/uv/python/cpython-3.12.13-linux-x86_64-gnu/lib/python3.12/socket.py", line 850, in create_connection sock.connect(sa) ConnectionRefusedError: [Errno 111] Connection refused - **Assistant:** WARNING | 2026-05-10 14:20:14,869 | angr.calling_conventions | Guessing call prototype. Please specify prototype. WARNING | 2026-05-10 14:20:14,884 | angr.storage.memory_mixins.default_filler_mixin | The program is accessing register with an unspecified value. This could indicate unwanted behavior. WARNING | 2026-05-10 14:20:14,884 | angr.storage.memory_mixins.default_filler_mixin | angr will cope with this by generating an unconstrained symbolic variable and continuing. You can resolve this by: WARNING | 2026-05-10 14:20:14,884 | angr.storage.memory_mixins.default_filler_mixin | 1) setting a value to the initial state WARNING | 2026-05-10 14:20:14,884 | angr.storage.memory_mixins.default_filler_mixin | 2) adding the state option ZERO_FILL_UNCONSTRAINED_{MEMORY,REGISTERS}, to make unknown regions hold null WARNING | 2026-05-10 14:20:14,884 | angr.storage.memory_mixins.default_filler_mixin | 3) adding the state option SYMBOL_FILL_UNCONSTRAINED_{MEMORY,REGISTERS}, to suppress these messages. WARNING | 2026-05-10 14:20:14,884 | angr.storage.memory_mixins.default_filler_mixin | Filling register rbp with 8 unconstrained bytes referenced from 0x4011ad (PLT.malloc+0xfd in round_01.bin (0x11ad)) WARNING | 2026-05-10 14:20:14,885 | angr.storage.memory_mixins.default_filler_mixin | Filling register rbx with 8 unconstrained bytes referenced from 0x4011b1 (PLT.malloc+0x101 in round_01.bin (0x11b1)) not found 0 1 0 - **Assistant:** WARNING | 2026-05-10 14:20:27,270 | angr.calling_conventions | Guessing call prototype. Please specify prototype. WARNING | 2026-05-10 14:20:27,285 | angr.storage.memory_mixins.default_filler_mixin | The program is accessing register with an unspecified value. This could indicate unwanted behavior. WARNING | 2026-05-10 14:20:27,285 | angr.storage.memory_mixins.default_filler_mixin | angr will cope with this by generating an unconstrained symbolic variable and continuing. You can resolve this by: WARNING | 2026-05-10 14:20:27,285 | angr.storage.memory_mixins.default_filler_mixin | 1) setting a value to the initial state WARNING | 2026-05-10 14:20:27,285 | angr.storage.memory_mixins.default_filler_mixin | 2) adding the state option ZERO_FILL_UNCONSTRAINED_{MEMORY,REGISTERS}, to make unknown regions hold null WARNING | 2026-05-10 14:20:27,285 | angr.storage.memory_mixins.default_filler_mixin | 3) adding the state option SYMBOL_FILL_UNCONSTRAINED_{MEMORY,REGISTERS}, to suppress these messages. WARNING | 2026-05-10 14:20:27,285 | angr.storage.memory_mixins.default_filler_mixin | Filling register rbp with 8 unconstrained bytes referenced from 0x4011ad (PLT.malloc+0xfd in round_01.bin (0x11ad)) WARNING | 2026-05-10 14:20:27,286 | angr.storage.memory_mixins.default_filler_mixin | Filling register rbx with 8 unconstrained bytes referenced from 0x4011b1 (PLT.malloc+0x101 in round_01.bin (0x11b1)) WARNING | 2026-05-10 14:20:27,409 | angr.storage.memory_mixins.default_filler_mixin | Filling memory at 0xc0000050 with 49 unconstrained bytes referenced from 0x500008 (strlen+0x0 in extern-address space (0x8)) 0 {'active': 1} ['0x4011e8'] 10 {'active': 1} ['0x40126e'] 20 {'active': 1} ['0x401080'] 30 {'active': 1} ['0x40126e'] 40 {'active': 1} ['0x401080'] 50 {'active': 1} ['0x40126e'] 60 {'active': 1} ['0x401080'] 70 {'active': 1} ['0x40126e'] 80 {'active': 1} ['0x401080'] 90 {'active': 1} ['0x40126e'] 100 {'active': 1} ['0x401080'] 110 {'active': 1} ['0x40126e'] 120 {'active': 1} ['0x401080'] 130 {'active': 1} ['0x40126e'] 140 {'active': 1} ['0x401080'] 150 {'active': 1} ['0x40126e'] 160 {'active': 1} ['0x401080'] 170 {'active': 1} ['0x40126e'] 180 {'active': 1} ['0x401080'] 190 {'active': 1} ['0x40126e'] - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 198, in main() File "/workspace/solve_empols.py", line 177, in main answer = answer_from_elf(elf) ^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 86, in answer_from_elf raise ValueError("no memcpy answer source found") ValueError: no memcpy answer source found - **Assistant:** The new failure is still the bytewise transform family, but GCC emitted `xor eax, imm8` (`83 f0 1d`) instead of `xor al, imm8`. I’m adding those equivalent encodings for xor/add/sub so the solver covers both compiler shapes. - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 207, in main() File "/workspace/solve_empols.py", line 175, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 19, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** The service is intermittently closing before it sends a binary, independent of the solver. I’m adding a small post-menu delay and retry loop around connection startup to reduce those aborted sessions. - **Assistant:** connect attempt 1 failed: [Errno 111] Connection refused menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 218, in main() File "/workspace/solve_empols.py", line 197, in main answer = answer_from_elf(elf) ^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 87, in answer_from_elf raise ValueError("no memcpy answer source found") ValueError: no memcpy answer source found - **Assistant:** The latest word-sum variant has an odd input length (94 bytes, 47 word pairs), so the two tables are not separated by a full equal-sized block. I’m changing that solver to count only the initialized pairs present in both tables instead of assuming the table bases define the length. - **Assistant:** menu received (2407 bytes) 01: b'PnNeJEDUeSjDLZGsURmgkhRPzVNpvyjJrqcvTnZcPfovpqDBpujaTWOmyVEywMnOSjhbVFNPWPOgjagPnnEYkQABbFYxjxVLbQMD' 02: b'ziP1Jf4KGJE34nnMqYr4WjOz8w817Wp6EsZVEqeh6PCFm8qFVDEEGEi7XotT5TPzmkfES6ryNwiQghPH61YXP8qcM' Traceback (most recent call last): File "/workspace/solve_empols.py", line 215, in main() File "/workspace/solve_empols.py", line 194, in main answer = answer_from_elf(elf) ^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 87, in answer_from_elf raise ValueError("no memcpy answer source found") ValueError: no memcpy answer source found - **Assistant:** Now the solver passed rounds 1 and 2, then hit another unseen template on round 3. I’m inspecting `round_03.bin` and adding that template. - **Assistant:** Round 3 is still the word-sum checker, but the compiler used the shorter 8-bit stack displacement encoding for the first table load. I’m generalizing the parser to accept both 8-bit and 32-bit displacements for both arrays. - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 232, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** menu received (2407 bytes) 01: b'NQGUrUXfaEvWUKgevxApvXRmfmnDOkHGZAkNziSoANlwHz' 02: b'NxYNO9YwGwf5qSrNZ3qrhLK2DgwZpNg3oGthMB' 03: b'n37AGmUvRs' Traceback (most recent call last): File "/workspace/solve_empols.py", line 232, in main() File "/workspace/solve_empols.py", line 213, in main raise ValueError(f"candidate for round {round_no:02d} failed local validation: {answer!r}") ValueError: candidate for round 04 failed local validation: b'OteQBhiGBAcyccBLTzXMDWob' - **Assistant:** The solver passed three rounds in the latest session. Round 4 produced a candidate that failed local validation, so the validation guard prevented a bad remote answer; I’m inspecting that binary to correct the parser. - **Assistant:** Round 4 is a `getcwd`-based template that does not consume `argv[1]`, so local “run with candidate as argv” is the wrong validation method for that family. The table solver still recovers the expected string; I’m disabling local argv validation for binaries importing `getcwd`. - **Assistant:** menu received (2407 bytes) 01: b'abVHohrZmkwhlMSNwpfpLcWgNlrytLRRRWOuIglyyaPuViEGUDjGivhyhEHyvIuYuUVq' 02: b'keUjBcmtaRaxWpusZbrDxxFStQbRGRbNkRrrNSvSkWTMVyjClDQQjX' Traceback (most recent call last): File "/workspace/solve_empols.py", line 232, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** The service closed after round 2, so the second answer was probably semantically wrong despite extracting a string. I’m checking whether round 2 was a `getcwd` template or another case where the candidate needs adjusted before submission. - **Assistant:** Round 2’s candidate locally validates and has the expected 54-byte length, so that closure was likely another service abort rather than a wrong answer. I’m rerunning; the solver is now covering the observed templates and checking argv-based ones locally. - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 232, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** The repeated aborts may be service instability, but the local execution checks and file writes also add avoidable latency. I’m switching the production run to in-memory solving only, with validation/saving available via environment variables when debugging. - **Assistant:** menu received (2407 bytes) 01: b'KZ6lck8YZU' 02: b'mKA5BNjBMt3wcMBrxAUdUkcDjFB0L0hkV4WMxx8Wm' 03: b'6dr5X08rEJ' 04: b'fErplTq3YQ' 05: b'LHuxyXdPR3' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** The fast run reached round 5, then the service closed. That suggests one of the first five answers was wrong under an unvalidated template. I’m rerunning with round saving and validation enabled to capture the failing binary precisely, accepting the extra latency for diagnosis. - **Assistant:** menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** menu received (2407 bytes) 01: b'vYXIaPfZMsAjsfrcjlRoRcgssjxDhPUgcLRKtEBTinuE' 02: b'TyrucyOsZVleqbcYbrJeJRXLDYxAPVxtBQPVAuLaDuOilglrzvvWhJUJqdRKFhRByFTxMMoi' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** The saved round 2 from the diagnostic run is not `getcwd` and locally validates, so the mid-session close still looks like service instability or a tight server-side timeout. I’m going back to fast mode and will retry full sessions until one completes. - **Assistant:** RUN:7 menu received (2407 bytes) 01: b'M0YDF9mVrdQDDq4VE1K0aogPAwmByaea0yjLwimC3Vzt8HkU3zl30g23CmKVr1MQ2Lu' 02: b'jxkb7XNBuk' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed RUN:8 menu received (2407 bytes) 01: b'oMwmL55BN2' 02: b'iWn1wXZ29fhpzCI1qTxMLzSoZwDFzJjiEPW8WNGbGwhDJdA3HKdpBDwgQvqq9MV38viwmQTQI3vkIh1iuBb' 03: b'Gh85JJQtui' 04: b'oxMWiQgwxqhBmUgREuYEbleDPhMeHKBdJdYiIRGgLQcOZvuBslmzvPeWgTAPoGHnXPKLZFDhltVkOummGsQyMEJBZg' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed RUN:9 menu received (2407 bytes) 01: b'zD7RB745em' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed RUN:10 menu received (2407 bytes) 01: b'a7gKX8iIO8' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** The random sessions show some answers are accepted and others close the connection, so there is at least one template whose extracted string is not the submitted answer. I’m running a save-only fast session so the exact last submitted binary is preserved when the service closes. - **Assistant:** connect attempt 1 failed: [Errno 111] Connection refused connect attempt 2 failed: [Errno 111] Connection refused connect attempt 3 failed: [Errno 111] Connection refused connect attempt 4 failed: [Errno 111] Connection refused menu received (2407 bytes) 01: b'5kiay3IooUCn2XH5XV4weHEVhIekmRjOTkAkV1TbG1ILbikNYehLSeSyMx1j5GqZ4R3D58ZBaEfLx6qacz48qokBBtqN' 02: b'CwYwMlYCjvHETmuNXOhiuqKAtnkcUbOQgNczCOEBcALIrgCiCafdjcewiJkvzFSLvKHQEpAtDAottthbRaxaZyvP' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError("connection closed") EOFError: connection closed - **Assistant:** I need to see the bytes sent just before a close; the current `recv_until` discards any “wrong” or status text if the socket closes before the next `ANSWER:`. I’m changing it to include the partial response in the exception so we can distinguish service aborts from rejected answers. - **Assistant:** connect attempt 1 failed: [Errno 111] Connection refused menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'\nSolve twenty random gzipped binaries...\n ' - **Assistant:** menu received (2407 bytes) 01: b'QcbBFKcoDnHaPvapTYomKgEVYXweIYfQvumFPKhfYYCyrnuaeFxpmaxXPK' 02: b'LpYlQ0lmN7rxT1oVAqHq5KgsKBkUxpJzp3gV6thuFdaCHbNZ0nY4NbWDGzW5TdoxGCE9PoHIUPmqp58eSb8yUUkAAX' 03: b'5jEmUh2K0jtw9mL6Mvic2pNkE1y3D64q9HpTC0QCXdb3Ew43iqHv17SOWd12Sk' 04: b'yApiTTbL13cKwVxlmPrp2BYNK3h0Gd9Y4hYpJD0V0e3OqLa9' 05: b'9S8qeX0afo' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' - **Assistant:** The saved closing session had all argv-based rounds locally valid; the close had no error bytes. I’m going to let fast retries run longer. If it fails on a reproducible template, the saved-round path is ready; if it’s transient, a clean 20-round run should eventually produce the flag. - **Assistant:** Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'\nSolve twenty random gzipped binaries...\n ' RUN:35 menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'\nSolve twenty random gzipped binaries...\n ' RUN:36 connect attempt 1 failed: [Errno 111] Connection refused connect attempt 2 failed: [Errno 111] Connection refused connect attempt 3 failed: [Errno 111] Connection refused connect attempt 4 failed: [Errno 111] Connection refused connect attempt 5 failed: [Errno 111] Connection refused menu received (2407 bytes) 01: b'ldFNsXSpvJiSwZUnqzoLFgOPmopuCKwQWlizkGZaUHuwhccdCHEbOYldDNSCOQjqRZkFnK' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:37 menu received (2407 bytes) 01: b'fYVYMO5Pbl' 02: b'A1iiwapB89FUeqbD6McsfFSUTCcsSUyEg4rlE6NlHLnEMurJKBxgabDScmve' 03: b'grvcAbzuaErosDIhHSbXuqCDsUEmzitOGZ' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:38 menu received (2407 bytes) 01: b'vm8ZgGtt2aDESVC55t5JnBX3hjrrrzj' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:39 menu received (2407 bytes) 01: b'siHIZGOx0mASjWxewrGUrMRmv1jTZZymHDo0Br3oOuDt' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:40 - **Assistant:** menu received (2407 bytes) 01: b'FOyX6jYDOmfCSLNN5wGYvjzSif9vgW6ZrRYgwA259fClokzaCTAIa0sFOnuIDT6PbE' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:41 menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'\nSolve twenty random gzipped binaries...\n ' RUN:42 menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'\nSolve twenty random gzipped binaries...\n ' RUN:43 menu received (2407 bytes) 01: b'HC3BsdnPNw' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:44 menu received (2407 bytes) 01: b'dG3W0fBUYJl9CI3XX3PcnFoqQXkEebNCKVVweaUtrd' 02: b'PVledkuBRrugGmfWiGuoulruknkkVrginSeQSKINNbayNxgwLsdNVjckcrIhOZMEYwHaCFDkCr' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:45 menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'\nSolve twenty random gzipped binaries...\n ' RUN:46 menu received (2407 bytes) 01: b'vYXIaPfZMsAjsfrcjlRoRcgssjxDhPUgcLRKtEBTinuE' 02: b'uI1KzBTzNm' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:47 menu received (2407 bytes) 01: b'FOyX6jYDOmfCSLNN5wGYvjzSif9vgW6ZrRYgwA259fClokzaCTAIa0sFOnuIDT6PbE' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:48 connect attempt 1 failed: [Errno 111] Connection refused connect attempt 2 failed: [Errno 111] Connection refused connect attempt 3 failed: [Errno 111] Connection refused menu received (2407 bytes) 01: b'HC3BsdnPNw' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' RUN:49 menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'\nSolve twenty random gzipped binaries...\n ' RUN:50 menu received (2407 bytes) Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'\nSolve twenty random gzipped binaries...\n ' - **Assistant:** The long retry confirms this is not just random instability; many sessions close immediately after a specific submitted answer. I’m going to capture a first-round close and validate that exact binary locally to identify the missing semantic case. - **Assistant:** menu received (2407 bytes) 01: b'fsfyyvMPhG' Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 200, in main transcript += recv_until(sock, b"ANSWER:") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 20, in recv_until raise EOFError(f"connection closed while waiting for {marker!r}; partial={data!r}") EOFError: connection closed while waiting for b'ANSWER:'; partial=b'' - **Assistant:** The first-round candidate `fsfyyvMPhG` locally returns the checker’s nonzero “match” code, yet the service closes. That suggests the service may define success as exit code 0, not the checker’s internal `1` path. I’m probing one session with a deliberately wrong first answer to confirm the convention. - **Assistant:** got first 5111 b'\nYOU FAIL\n' len 10 - **Assistant:** The probe with `AAAA` returned `YOU FAIL`, while correct-looking answers lead to a silent close while waiting for the next binary. That points to accepted answers followed by backend/session aborts, not ordinary rejection. I’m pausing briefly to avoid hammering the service, then I’ll try a single clean run. - **Assistant:** connect attempt 1 failed: [Errno 111] Connection refused connect attempt 2 failed: [Errno 111] Connection refused connect attempt 3 failed: [Errno 111] Connection refused Traceback (most recent call last): File "/workspace/solve_empols.py", line 233, in main() File "/workspace/solve_empols.py", line 193, in main menu = recv_until(sock, b"2) Play") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/workspace/solve_empols.py", line 18, in recv_until chunk = sock.recv(65536) ^^^^^^^^^^^^^^^^ ConnectionResetError: [Errno 104] Connection reset by peer - **Assistant:** After cooldown the service is now refusing/resetting connections before the menu completes, so it looks rate-limited or unstable from this container. I have the solver in place; I’ll make one more attempt with a longer backoff. - **Assistant:** menu received (2407 bytes) 01: b'5jEmUh2K0jtw9mL6Mvic2pNkE1y3D64q9HpTC0QCXdb3Ew43iqHv17SOWd12Sk' 02: b'NkTdKFmCmitfhjnDdKkcUCJcIwQvemCTqUgBIlhGdvLm' 03: b'yIXlkRuLmCanXWnrWTITJipnVegItrTdcPlOppalWQtRRBgCmjlCcFVvXiJSYirRqAiAQzfcSgkxQxrb' 04: b'lS5ymzLrD4D9v3Eo8GqcCSikUf5A3OPPjf1l1zBjsrdMMkkp1ueOCHMWboOWM3sJhxMKG3h24ce6' 05: b'XuEabJGZ0vJiiXSrTp8OgibA5cQnCYpvWh4sZDHYnxdoiZOvCMHb0mx9BcDQzxp68NOvx90KBgA4qIxJhluHMKjXDr7FNQ6' 06: b'iWn1wXZ29fhpzCI1qTxMLzSoZwDFzJjiEPW8WNGbGwhDJdA3HKdpBDwgQvqq9MV38viwmQTQI3vkIh1iuBb' 07: b'JXwUHUuERWVLUbaLciuqRMZtQbzGqr' 08: b'oBBdsqgtyLyHwfpbtHpeFkcFEwFxATgaEvTbFPxyfostKqFTEuvDtJNHsBVUNA' 09: b'axPAFcWXbrvbLgmZmihZeYZAaYLnxLVoBMtyNSHtAGgwVcniFbvPuIjfWSEeUSxiFOzZAURlYE' 10: b'6qdv1gBPoL' 11: b'Qk8m8OoquheJ5pO4uRfNQYhaAil5Z49hJTs' 12: b'ZzuK71UOmw' 13: b'sXrl28V3wvpJS2ZRouqFTz9qtGYe2nPbE7s5YzBiMCi6KXaVPBidDylPrSJNY49DZ70tSFM' 14: b'fYVYMO5Pbl' 15: b'ACWkOUkZbwgDUWGyDJUkwaahkdlmKrNNZoYD' 16: b'69JJI1IKC6Av4MiX8Oe9hKYDUVDYW8pBiZv39BfjtAVvEKK2' 17: b'Rx0INfgqGN39uR3Ujgx38F2E9aKjLeqjRhoiCYOaj5oozcXAfU9WfVUGZjinxYWn9z4AEB6' 18: b'UzXhQCwEcrtpXLoONYaUBOJZKJWvDArlZgRTNLmIkfwxZbgLHunfMIeDKHswimtoWboHcVZZzGdIIkUj' 19: b'4OcFCxfcRf' 20: b'6UbtEw7GWZvg03wcAR1QTMFa6SsDnXOiti315BO8bYBsZFeIaz4CooMguJvJMVSZG2AZ1eqPTacz1YpnMaYWD9NZeBcW1kV5B' b'midnight{y0u_4r3_th3_m4st3r_0f_sl0ps0lv3s}' - **Assistant:** Solved. Flag: ```text midnight{y0u_4r3_th3_m4st3r_0f_sl0ps0lv3s} ``` I left the working solver at [solve_empols.py](/workspace/solve_empols.py). The service sends each challenge as hex-encoded gzip containing a small ELF. The solver decodes each ELF and handles the observed generated checker templates: - direct `strcmp` against a string in `.rodata` - bytewise xor/add/sub checks against stack constants - 16-bit pair checks where `input_word + table_a[i] == table_b[i]` - `getcwd`-style symbolic/environment templates by extracting the same encoded target tables Each derived answer is submitted back to the TCP service for 20 rounds. The service was flaky and often reset after accepted answers, but a longer-backoff run completed and returned the flag. I also posted the final findings to the requested Discord webhook. - **System:** Thread completed