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.
Fixed in zeroconf 0.149.5 (PR #1719).
Upgrade to >= 0.149.5.
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.
No EPSS score in this advisory JSON.
| Base score | Version | Severity | Vector |
|---|---|---|---|
| 6.5 | 3.1 | — |
|
| Type | Value |
|---|---|
| GHSA | GHSA-9pgc-3ccv-5297 ↗ |
| CVE | CVE-2026-47180 ↗ |
| CWE id | Name |
|---|---|
| CWE-674 | Uncontrolled Recursion |
Vulnerable version ranges and first patched releases as published by GitHub.
| Ecosystem | Package | Vulnerable range | First patched | Vulnerable functions |
|---|---|---|---|---|
| pip | zeroconf | < 0.149.5 | 0.149.5 | — |