{"id":"CVE-2026-47180","aliases":["GHSA-9pgc-3ccv-5297","PYSEC-2026-3436"],"title":"zeroconf has unbounded recursion in DNS compression-pointer decoder that allows LAN-local denial of service","summary":"zeroconf has unbounded recursion in DNS compression-pointer decoder that allows LAN-local denial of service","severity":"medium","cvss":6.5,"cvssVector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","vendor":"zeroconf","product":"zeroconf","ecosystem":"pip","affected":["zeroconf < 0.149.5"],"patched":["zeroconf 0.149.5"],"published":"2026-05-29","updated":"2026-07-13","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-9pgc-3ccv-5297","references":[{"url":"https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-9pgc-3ccv-5297"},{"url":"https://github.com/python-zeroconf/python-zeroconf/issues/1713"},{"url":"https://github.com/python-zeroconf/python-zeroconf/pull/1719"},{"url":"https://github.com/python-zeroconf/python-zeroconf"}],"tags":["osv","pip"],"ingestedAt":"2026-07-13T18:57:56.050Z","epss":0.0037,"epssPercentile":0.30892,"slug":"CVE-2026-47180","body":"## Overview\n\n### 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)\n\n## Affected packages\n\n- `zeroconf < 0.149.5`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `zeroconf 0.149.5`","depth":"sunlit","depthScore":36,"depthScoreParts":{"impact":35.8,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}