GHSA-9pgc-3ccv-5297 zeroconf has unbounded recursion in DNS compression-pointer decoder that allows LAN-local denial of service

• PyPI zeroconf: < 0.149.5 → fixed in 0.149.5

Impact `DNSIncoming._decode_labels_at_offset` recurses once per DNS-name compression pointer (RFC 1035 §4.1.4). Pointer cycles and label counts were capped, but the chain length of unique forward pointers was not. A single ~3 kB mDNS packet carrying ~1500 chained pointers drives the recursion past CPython's default limit, and `RecursionError` was not listed in `DECODE_EXCEPTIONS`, so it escaped `DNSIncoming.__init__` and was logged by asyncio's default exception handler. Any unauthenticated host on the local link (UDP/5353, `224.0.0.251` / `ff02::fb`) can degrade the mDNS listener; that includes a guest on the same Wi-Fi, a compromised IoT device, or a container on a shared bridge. Replaying at a few hertz produces sustained CPU burn and log flooding, and mDNS-dependent features (HomeKit, Chromecast/Matter, AirPlay, printers) degrade while the attack is in flight. Patches Fixed in `zeroconf` 0.149.5 (PR #1719). Upgrade to `>= 0.149.5`. Workarounds There is no in-process workaround; upgrading is the fix. Otherwise, restrict mDNS (UDP/5353) to trusted Layer-2 segments via AP client isolation, guest-network separation, or host firewall rules. Resources • PR #1719, fix • Issue #1713, public tracking issue • RFC 1035 §4.1.4, RFC 6762, CWE-674