Carrier - SEC-T CTF 2026 Writeup
Description
The modem came out of a box in the basement, and the number came with it, written on the underside of the case in pencil.
ATDT08556677
Somebody in Stockholm still runs a board on it, and still lets strangers apply for an account. Nothing else is written on the case. The other numbers are on the boards.
Type ATDT and a number to dial; spaces and dashes in the number are ignored, the way a real one ignores them. Logging off a board drops the carrier and puts you back on the modem, and +++ then ATH does the same in a hurry.
The boards answer in ANSI at 2400 baud. Bring a terminal that can take it.
nc sec-t-challenges.se 10003
Solution
Connecting to a BBS over this service needs a terminal that handles ANSI well.
icy_tools includes Icy_Term, which
works for this purpose.
After connecting to the challenge service with Icy_Term, we dial the board
with ATDT08556677.
The board presents a menu to login, apply, check, or disconnect.
We choose apply and register a new user. After the ANSI splash screens, the
main menu appears. Pressing ? lists the available options.
From here, m opens the message area. A newscan walks the unread messages on
the board.
Reading through the messages:
The flag appears in one of the messages.
Flag: SECT{last_night_a_demoscener_saved_my_life}