# Thread Handoff - Thread: nimble-packet-8111 - UUID: dc131c8f-bb4f-4366-92fb-f20d02553a74 - CTF: midnight-sun-ctf-2026-quals - Challenge: smachine - Runtime: codex - Model: gpt-5.5 - Status: completed ## Transcript - **Assistant:** I’ll inspect the local challenge files first, then connect to the service and treat it as a black-box protocol. I’ll also post concise progress updates to the provided webhook when network access is available. - **Assistant:** There’s only a tiny local hint file, so the real surface is the remote service. I’m reading that hint and then I’ll start probing the TCP interaction. - **Assistant:** The service accepts a TCP connection but gave no banner on a plain `nc` probe. I’m switching to scripted socket probes so I can control timeouts and input precisely. - **User:** do not port scan - **Assistant:** Understood. I won’t scan ports; I’ll only interact with the single challenge endpoint `smachine.play.ctf.se:9189`. - **Assistant:** Traceback (most recent call last): File "", line 2, in 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) TimeoutError: timed out - **Assistant:** nc: connect to smachine.play.ctf.se (13.60.76.107) port 9189 (tcp) timed out: Operation now in progress - **Assistant:** DNS resolves to `13.60.76.107`, but the endpoint is timing out on connect from this container. I’ll retry the same single service with a longer timeout before deciding whether the remote is down or filtered. - **Assistant:** nc: connect to smachine.play.ctf.se (13.60.76.107) port 9189 (tcp) failed: Connection refused - **Assistant:** nc: connect to smachine.play.ctf.se (13.60.76.107) port 9189 (tcp) failed: Connection refused - **Assistant:** Connection to 13.60.76.107 9189 port [tcp/*] succeeded! ▄▄█████████ ▄███▄ ▄▄███ ▄▄████████▄ ▄▄████████▄ ████▀▀▀▀▀▀▀ ██████▄██████ ████▀▀▀████ ████▀▀▀████ ████▄▄▄▄▄▄ ████▀███▀████ ████▄▄▄████ ████ ▀▀▀▀ ▀▀▀▀▀▀▀████ ████ ▀▀▀ ████ ████▀▀▀████ ████ ▄▄▄▄ ▄▄▄▄▄▄▄████ ████ ████ ████ ████ ████▄▄▄████ ██████████▀ ████ ████ ████ ████ ▀█████████��� ▀▀▀▀▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀ ▄███ ▄███ ▄█████████ ▄███ ▄███ ▄▄█████████ ████ ████ ▀▀▀████▀▀▀ █████▄ ████ ████▀▀▀▀▀▀▀ ████▄▄▄████ ████ ███████████ ████▄▄▄ ████▀▀▀████ ████ ████▀▀█████ ████▀▀▀ ████ ████ ▄▄▄████▄▄▄ ████ ▀████ ████▄▄▄▄▄▄▄ ████ ████ ██████████ ████ ████ ▀██████████ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀ Welcome to the Simple Machine. Type help or ? to list operations. #> - **Assistant:** Direct-IP connection works and the service banner says “Welcome to the Simple Machine. Type help or ? to list operations.” I’ll now enumerate commands against that one service and keep the interaction controlled. - **Assistant:** initial: --- send help --- send ? - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused - **Assistant:** The service is intermittent: one direct connection reached the prompt, then later attempts returned connection refused. I’m going to keep retries sparse against the same port and capture the full help output once it comes back. - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused - **Assistant:** Connection to 13.60.76.107 9189 port [tcp/*] succeeded! - **Assistant:** ? - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused - **Assistant:** The endpoint behavior looks unstable under repeated connections: refused, timeout, and sometimes accepted without response. I’m limiting retries and will use the first responsive session to gather the command set rather than fuzz blindly. - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused Connection to 13.60.76.107 9189 port [tcp/*] succeeded! ▄▄█████████ ▄███▄ ▄▄███ ▄▄████████▄ ▄▄████████▄ ████▀▀▀▀▀▀▀ ██████▄██████ ████▀▀▀████ ████▀▀▀████ ████▄▄▄▄▄▄ ████▀███▀████ ████▄▄▄████ ████ ▀▀▀▀ ▀▀▀▀▀▀▀████ ████ ▀▀▀ ████ ████▀▀▀████ ████ ▄▄▄▄ ▄▄▄▄▄▄▄████ ████ ████ ████ ████ ████▄▄▄████ ██████████▀ ████ ████ ████ ████ ▀█████████��� ▀▀▀▀▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀ ▄███ ▄███ ▄█████████ ▄███ ▄███ ▄▄█████████ ████ ████ ▀▀▀████▀▀▀ █████▄ ████ ████▀▀▀▀▀▀▀ ████▄▄▄████ ████ ███████████ ████▄▄▄ ████▀▀▀████ ████ ████▀▀█████ ████▀▀▀ ████ ████ ▄▄▄████▄▄▄ ████ ▀████ ████▄▄▄▄▄▄▄ ████ ████ ██���███████ ████ ████ ▀██████████ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀ Welcome to the Simple Machine. Type help or ? to list operations. #> #> - **Assistant:** ERR TimeoutError('timed out') attempt 2 ERR TimeoutError('timed out') attempt 3 ERR ConnectionRefusedError(111, 'Connection refused') attempt 4 ERR ConnectionRefusedError(111, 'Connection refused') attempt 5 ERR TimeoutError('timed out') attempt 6 ERR TimeoutError('timed out') attempt 7 ERR TimeoutError('timed out') attempt 8 ERR ConnectionRefusedError(111, 'Connection refused') - **Assistant:** The service seems more responsive through `nc` than Python sockets from this environment, so I’m switching to delayed `nc` input: connect, wait for the banner/prompt, then send commands. This avoids racing input before the program is ready. - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused Connection to 13.60.76.107 9189 port [tcp/*] succeeded! - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused Connection to 13.60.76.107 9189 port [tcp/*] succeeded! - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused Connection to 13.60.76.107 9189 port [tcp/*] succeeded! - **Assistant:** Connection to smachine.play.ctf.se (13.60.76.107) 9189 port [tcp/*] succeeded! - **Assistant:** nc: connect to 13.60.76.107 port 9189 (tcp) failed: Connection refused - **Assistant:** HTTP/2 404 date: Sun, 10 May 2026 18:06:41 GMT content-type: text/plain; charset=utf-8 content-length: 19 x-content-type-options: nosniff cf-cache-status: DYNAMIC nel: {"report_to":"cf-nel","success_fraction":0.0,"max_age":604800} report-to: {"group":"cf-nel","max_age":604800,"endpoints":[{"url":"https://a.nel.cloudflare.com/report/v4?s=91w%2Bo1cHpWPDMMwMgvVcBEt8E8Lkg36tpTJ3x0bItifs0bMpNZzaYTa0sJEhskIA6ut5BMYZs4naPmy0YgVkrmKe1s5M09okBRoJpHYVIOwwuEZaMIMIL8s%3D"}]} server: cloudflare cf-ray: 9f9ae114ae00aec4-HKG alt-svc: h3=":443"; ma=86400 - **User:** tcp 성공 이후 다시 시도하려고 하지 말고 한번에 계속 다시 시도하자고.. 서버가 불안정해 - **Assistant:** 맞아요. 연결 성공 뒤에 끊고 다시 붙는 방식이 문제였습니다. 이제는 연결이 성립된 프로세스 안에서 입력을 계속 흘려보내는 방식으로 바꾸겠습니다. - **Assistant:** curl: (28) Time-out - **Assistant:** 2026/05/10 18:07:34 socat[379] N successfully connected to 13.60.76.107:9189 2026/05/10 18:07:34 socat[379] N starting data transfer loop with FDs [0,1] and [5,5] 2026/05/10 18:07:48 socat[379] N socket 1 (fd 0) is at EOF 2026/05/10 18:07:48 socat[379] N exiting with status 0 - **Assistant:** 2026/05/10 18:08:13 socat[384] W connecting to AF=2 13.60.76.107:9189: Connection timed out 2026/05/10 18:08:13 socat[384] E TCP:13.60.76.107:9189: Operation now in progress 2026/05/10 18:08:13 socat[384] N exit(1) - **Assistant:** 지금 `socat`을 `retry=100`으로 걸어 두어서 TCP 연결이 잡히기 전까지만 재시도하고, 연결되면 같은 세션을 계속 유지하게 했습니다. 아직은 timeout만 나오고 있어서 연결 성공 메시지를 기다리는 중입니다. - **Assistant:** 2026/05/10 18:12:51 socat[390] E read(5, 0x55df72846000, 8192): Connection reset by peer 2026/05/10 18:12:51 socat[390] N exit(1) - **Assistant:** ^C - **Assistant:** 한 가지 차이가 보입니다. `curl telnet://...`는 배너를 잘 받는데 raw `socat`/Python은 자주 무응답입니다. `curl`의 telnet 모드가 먼저 보내는 협상 바이트가 트리거일 수 있어서, 로컬에서 그 바이트를 확인한 뒤 같은 세션 방식으로 재현해 보겠습니다. - **Assistant:** curl: (28) Time-out - **Assistant:** ^C - **Assistant:** 로컬 확인상 `curl telnet://`가 특별한 협상 바이트를 보내지는 않았습니다. 결국 “좋은” backend에 붙었을 때만 배너가 오는 형태라서, 배너가 실제로 도착한 연결을 잡으면 그 연결에서 바로 `help`를 보내는 스크립트로 진행합니다. - **Assistant:** [err] ConnectionRefusedError(111, 'Connection refused') [attempt 2] [err] TimeoutError('timed out') [attempt 3] [err] OSError(113, 'No route to host') [attempt 4] [err] OSError(113, 'No route to host') [attempt 5] [err] OSError(113, 'No route to host') [attempt 6] [err] OSError(113, 'No route to host') [attempt 7] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 8] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 9] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 10] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 11] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 12] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 13] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 14] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 15] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 16] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 17] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 18] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 19] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 20] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 21] [tcp connected; waiting for banner] ▄▄█████████ ▄███▄ ▄▄███ ▄▄████████▄ ▄▄████████▄ ████▀▀▀▀▀▀▀ ██████▄██████ ████▀▀▀████ ████▀▀▀████ ████▄▄▄▄▄▄ ████▀███▀████ ████▄▄▄████ ████ ▀▀▀▀ ▀▀▀▀▀▀▀████ ████ ▀▀▀ ████ ████▀▀▀████ ████ ▄▄▄▄ ▄▄▄▄▄▄▄████ ████ ████ ████ ████ ████▄▄▄████ ██████████▀ ████ ████ ████ ████ ▀█████████▀ ▀▀▀▀▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀ ▄███ ▄███ ▄█████████ ▄███ ▄███ ▄▄█████████ ████ ████ ▀▀▀████▀▀▀ █████▄ ████ ████▀▀▀▀▀▀▀ ████▄▄▄████ ████ ███████████ ████▄▄▄ ████▀▀▀████ ████ ████▀▀█████ ████▀▀▀ ████ ████ ▄▄▄████▄▄▄ ████ ▀████ ████▄▄▄▄▄▄▄ ████ ████ ██���███████ ████ ████ ▀██████████ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀ Welcome to the Simple Machine. Type help or ? to list operations. #> [SEND b'help\r\n'] Documented commands (type help ): ======================================== add and help mul or regs sub win xor #> [SEND b'?\r\n'] Documented commands (type help ): ======================================== add and help mul or regs sub win xor #> - **Assistant:** 잡았습니다. 좋은 연결에서 `help` 결과가 나왔고 명령은 `add and help mul or regs sub win xor`입니다. 다음에는 같은 방식으로 배너가 온 연결을 잡은 뒤 각 help topic과 `regs`/`win` 동작을 한 세션에서 뽑겠습니다. - **Assistant:** [err] ConnectionRefusedError(111, 'Connection refused') [attempt 2] [err] ConnectionRefusedError(111, 'Connection refused') [attempt 3] --- BANNER OK --- >>> help add add value to register, e.g add x0 1 | add x0 x1. #> >>> help sub sub value to register, e.g sub x0 1 | sub x0 x1. #> >>> help mul multiply value to register, e.g mul x0 1 | mul x0 x1. #> >>> help and and value to register, e.g and x0 1 | and x0 x1. #> >>> help or or value to register, e.g or x0 1 | or x0 x1. #> >>> help xor xor value to register, e.g xor x0 1 | xor x0 x1. #> >>> help regs show registers. #> >>> help win check if you have won. #> >>> regs x0 = 0x0000 x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> win Set any register to 0x1337 in order to win. #> - **Assistant:** The machine is simple: ten 16-bit-looking registers `x0..x9`, all start at zero, and `win` says any register must become `0x1337`. I’m testing the shortest path first: add the target constant, then call `win`. - **Assistant:** The solve script is still retrying for a responsive banner; several TCP connects are either refused or connect without producing the prompt. I’m leaving it running rather than restarting after every partial connection. - **Assistant:** [attempt] 73 [attempt] 74 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 75 [attempt] 76 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 77 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 78 [attempt] 79 [attempt] 80 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 81 [attempt] 82 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 83 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 84 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 85 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 86 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 87 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 88 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 89 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 90 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 91 [err] ConnectionRefusedError(111, 'Connection refused') [attempt] 92 BANNER OK >>> add x0 0x1337 Invalid Syntax #> >>> regs x0 = 0x0000 x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> win Set any register to 0x1337 in order to win. #> - **Assistant:** `0x1337` as an immediate is rejected (`Invalid Syntax`), so the parser likely accepts decimal literals only. `0x1337` is decimal `4919`; I’ll set `x0` with `add x0 4919`, verify registers, then call `win`. - **Assistant:** BANNER OK >>> add x0 4919 Bad Result. #> >>> regs x0 = 0x0000 x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> win Set any register to 0x1337 in order to win. #> - **Assistant:** Decimal syntax is accepted, but `add x0 4919` returns `Bad Result` and leaves registers unchanged. That suggests each operation has a result constraint, likely immediate/register bounds or blocked direct target. I’ll probe valid small operations and register width behavior in one session. - **Assistant:** BANNER OK >>> add x0 1 #> >>> regs x0 = 0x0001 x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> add x0 2 #> >>> regs x0 = 0x0003 x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> mul x0 3 #> >>> regs x0 = 0x0009 x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> sub x0 1 #> >>> regs x0 = 0x0008 x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> xor x0 7 #> >>> regs x0 = 0x000f x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> or x1 4919 #> >>> regs x0 = 0x000f x1 = 0x1337 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> add x1 255 #> >>> regs x0 = 0x000f x1 = 0x1436 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> add x1 256 #> >>> regs x0 = 0x000f x1 = 0x1536 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> add x1 4096 #> >>> regs x0 = 0x000f x1 = 0x2536 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> - **Assistant:** Found the trick: `add` refuses to produce `0x1337` directly (`Bad Result`), but bitwise `or` from zero accepts decimal `4919` and sets the register to `0x1337`. I’ll run a clean `or x0 4919; win` session now. - **Assistant:** BANNER OK >>> or x0 4919 #> >>> regs x0 = 0x1337 x1 = 0x0000 x2 = 0x0000 x3 = 0x0000 x4 = 0x0000 x5 = 0x0000 x6 = 0x0000 x7 = 0x0000 x8 = 0x0000 x9 = 0x0000 #> >>> win You Win, Flag is midnight{s1MpL3_sT4cK_M4cH1N3} FLAG: midnight{s1MpL3_sT4cK_M4cH1N3} - **Assistant:** Solved. Flag: ```text midnight{s1MpL3_sT4cK_M4cH1N3} ``` Explanation: the service is a tiny register machine. `win` says any register must be `0x1337`. Directly doing `add x0 4919` is rejected with `Bad Result`, but bitwise operations are allowed. Since registers start at zero, this works: ```text or x0 4919 win ``` `4919` is decimal for `0x1337`, so `or x0 4919` sets `x0 = 0x1337`, and `win` prints the flag. - **System:** Thread completed