{"id":"CVE-2026-47180","aliases":["GHSA-9pgc-3ccv-5297","PYSEC-2026-3436"],"url":"https://o3.security/vulnerability/CVE-2026-47180","summary":"Zeroconf: Unbounded recursion in DNS compression-pointer decoder allows LAN-local denial of service","details":"### Impact\n\n`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.\n\nAny 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.\n\n### Patches\nFixed in `zeroconf` 0.149.5 ([PR #1719](https://github.com/python-zeroconf/python-zeroconf/pull/1719)).\nUpgrade to `>= 0.149.5`.\n\n### Workarounds\nThere 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.\n\n### Resources\n- [PR #1719](https://github.com/python-zeroconf/python-zeroconf/pull/1719), fix\n- [Issue #1713](https://github.com/python-zeroconf/python-zeroconf/issues/1713), public tracking issue\n- [RFC 1035 §4.1.4](https://www.rfc-editor.org/rfc/rfc1035#section-4.1.4), [RFC 6762](https://www.rfc-editor.org/rfc/rfc6762), [CWE-674](https://cwe.mitre.org/data/definitions/674.html)","published":"2026-07-17T18:21:25.199Z","modified":"2026-08-19T03:48:18.124161612Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.00226,"percentile":0.1361,"asOf":"2026-08-20"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"zeroconf","fixedVersion":"0.149.5"}],"fix":{"url":"https://github.com/python-zeroconf/python-zeroconf/commit/f9e23592137f30fdf7ef710dba065da31c79b1cf","label":"python-zeroconf/python-zeroconf@f9e2359"},"references":[{"type":"WEB","url":"https://github.com/python-zeroconf/python-zeroconf/releases/tag/0.149.5"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47180.json"},{"type":"ADVISORY","url":"https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-9pgc-3ccv-5297"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47180"},{"type":"FIX","url":"https://github.com/python-zeroconf/python-zeroconf/commit/f9e23592137f30fdf7ef710dba065da31c79b1cf"},{"type":"FIX","url":"https://github.com/python-zeroconf/python-zeroconf/pull/1719"},{"type":"WEB","url":"https://github.com/python-zeroconf/python-zeroconf/issues/1713"},{"type":"PACKAGE","url":"https://github.com/python-zeroconf/python-zeroconf"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-19T03:48:18.124161612Z"}}