GHSA-mxwc-wh95-pw4g

## Summary `trapster.libs.dns.decode_labels()` decodes DNS names from attacker-supplied UDP packets and recurses **once per RFC 1035 compression pointer** with **no cycle detection and no depth bound**. A single unauthenticated UDP datagram sent to the DNS honeypot drives the function past CPython's recursion limit, raising `RecursionError`. That exception is not handled anywhere on the `datagram_received` path, so it escapes into the asyncio event loop's default exception handler, the per-packet proxy task is never created, and a low-rate flood produces sustained CPU burn and log flooding (denial of service of the DNS honeypot module). ## Severity Medium (CVSS:3.1 `AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`). Network-reachable, unauthenticated, single-packet, availability-only against the DNS honeypot listener. ## Affected component - File: `trapster/libs/dns.py`, function `decode_labels()` (called by `decode_question_section` → `decode_dns_message`). - Reached from: `trapster/modules/dns.py`, `DnsUdpProtocol.datagram_received()` → `dns.decode_dns_message(data)`, where `data` is the raw attacker UDP payload received by `DnsHoneypot` on its configured bind address/port. - Version tested: latest `main` at commit `23156739de23816657cbc4582ad32094ed1cab43`. ## Details `decode_labels` implements RFC 1035 §4.1.4 name compression: ```python def decode_labels(message, offset): labels = [] while True: length, = struct.unpack_from("!B", message, offset) if (length & 0xC0) == 0xC0: pointer, = struct.unpack_from("!H", message, offset) offset += 2 return labels + decode_labels(message, pointer & 0x3FFF), offset # <-- recurses per pointer ... ``` Each compression pointer triggers a fresh recursive call to `decode_labels`. There is: - **No cycle detection** — a pointer that targets its own offset recurses forever. - **No depth bound** — a chain of distinct forward pointers recurses once per pointer. Either