{"id":"CVE-2026-47184","aliases":["GHSA-rfg2-pjw2-56x2","PYSEC-2026-3439"],"url":"https://o3.security/vulnerability/CVE-2026-47184","summary":"Zeroconf: Unbounded DNS record cache allows LAN-local memory exhaustion via multicast flood","details":"### Impact\n\n`DNSCache._async_add` inserted every response record into `cache`, `_expirations`, `_expire_heap`, and `service_cache` with no cap on entry count. The only pre-existing protection was a PTR TTL floor (`_DNS_PTR_MIN_TTL = 1125` s, RFC 6762 §10), which actually *prolonged* attacker-injected records, and a periodic `async_expire` on `_CACHE_CLEANUP_INTERVAL = 10` s that could not keep up with a flood.\n\nAny unauthenticated host on the local link (UDP/5353, `224.0.0.251` / `ff02::fb`) can multicast valid mDNS responses with unique names (RFC 6762 §11 allows up to 253 bytes each) and watch them accumulate. On memory-constrained deployments (Home Assistant on Raspberry-Pi-class hardware is the canonical victim) sustained traffic OOM-kills the process; under lighter load, every cache lookup and every periodic expiry pass grows linearly slower, starving asyncio and breaking unrelated zeroconf consumers (discovery, registration, ServiceBrowser callbacks). A second variant — re-multicasting cached records with shifting TTLs — grows `_expire_heap` unbounded between cleanup runs without touching `cache` or `_total_records`.\n\n### Patches\n\nFixed in `zeroconf` 0.149.6 ([PR #1718](https://github.com/python-zeroconf/python-zeroconf/pull/1718)). Upgrade to `>= 0.149.6`.\n\n### Workarounds\n\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\n- [PR #1718](https://github.com/python-zeroconf/python-zeroconf/pull/1718), fix\n- [Issue #1715](https://github.com/python-zeroconf/python-zeroconf/issues/1715), public tracking issue\n- [RFC 6762 §10](https://www.rfc-editor.org/rfc/rfc6762#section-10), [RFC 6762 §11](https://www.rfc-editor.org/rfc/rfc6762#section-11), [CWE-400](https://cwe.mitre.org/data/definitions/400.html)","published":"2026-07-17T18:25:07.387Z","modified":"2026-08-19T03:48:18.126534861Z","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":0.00389,"percentile":0.32687,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"zeroconf","fixedVersion":"0.149.7"}],"fix":{"url":"https://github.com/python-zeroconf/python-zeroconf/commit/0ad3f37b5b852b8f614d322283d148efb2cef6e4","label":"python-zeroconf/python-zeroconf@0ad3f37"},"references":[{"type":"WEB","url":"https://github.com/python-zeroconf/python-zeroconf/releases/tag/0.149.7"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47184.json"},{"type":"ADVISORY","url":"https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-rfg2-pjw2-56x2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47184"},{"type":"REPORT","url":"https://github.com/python-zeroconf/python-zeroconf/issues/1715"},{"type":"FIX","url":"https://github.com/python-zeroconf/python-zeroconf/commit/0ad3f37b5b852b8f614d322283d148efb2cef6e4"},{"type":"FIX","url":"https://github.com/python-zeroconf/python-zeroconf/pull/1718"},{"type":"PACKAGE","url":"https://github.com/python-zeroconf/python-zeroconf"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-19T03:48:18.126534861Z"}}