zeroconf has unbounded DNS record cache that allows LAN-local memory exhaustion via multicast flood
Impact
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.
Any 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.
Patches
Fixed in zeroconf 0.149.6 (PR #1718). Upgrade to >= 0.149.6.
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 #1718, fix
- Issue #1715, public tracking issue
- RFC 6762 §10, RFC 6762 §11, CWE-400
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | zeroconf | < 0.149.7 | 0.149.7 |
References
- https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-rfg2-pjw2-56x2
- https://github.com/python-zeroconf/python-zeroconf/issues/1715
- https://github.com/python-zeroconf/python-zeroconf/pull/1718
- https://github.com/python-zeroconf/python-zeroconf
- https://pypi.org/project/zeroconf
- https://github.com/advisories/GHSA-rfg2-pjw2-56x2
- https://nvd.nist.gov/vuln/detail/CVE-2026-47184
- CVSS vector
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-400, CWE-770- Platform
- Python (PyPI)
- Package
zeroconf- Disclosed
- 29.05.2026
- Updated
- 11.10.2026 14:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-3439 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-rfg2-pjw2-56x2 - CC BY 4.0
Vulnerability history: zeroconf
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 5
- First → latest
- 05.2026 06.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Medium 5
Disclosures per year
- 2026: 5
-
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