python-zeroconf: Unbounded TC-deferred queue allows LAN-local memory exhaustion via spoofed-source flood
Impact
AsyncListener.handle_query_or_defer retained every truncated (TC-bit) incoming query in self._deferred[addr] and armed a per-addr timer in self._timers[addr] that flushed the reassembled query within ~500 ms (RFC 6762 §18.5). Neither the per-addr list nor the number of distinct addr keys was capped, and the dedup check (for incoming in reversed(deferred): if incoming.data == msg.data) ran O(N) over the per-addr list on every arrival.
Any unauthenticated host on the local link (UDP/5353, 224.0.0.251 / ff02::fb) can stream byte-distinct TC-flagged mDNS queries — each up to _MAX_MSG_ABSOLUTE = 8966 bytes, with DNSIncoming retaining the raw data buffer plus parsed-record state. Trivially spoofed source IPs multiply the effect across _deferred / _timers, and the O(N) data compare burns CPU quadratically as each per-addr queue grows. On memory-constrained deployments (Home Assistant on Raspberry-Pi-class hardware is the canonical victim) sustained traffic OOM-kills the process; under lighter load, the per-arrival scan and event-loop scheduler starvation break unrelated zeroconf consumers (discovery, registration, ServiceBrowser callbacks).
Patches
Fixed in zeroconf 0.149.12 (PR #1751). Upgrade to >= 0.149.12.
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 #1751, fix
- RFC 6762 §18.5, CWE-400
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | zeroconf | < 0.149.12 | 0.149.12 |
References
- https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-9663-mqmp-p9mm
- https://github.com/python-zeroconf/python-zeroconf/pull/1751
- https://github.com/python-zeroconf/python-zeroconf/commit/b22c8ff19c66c68907d220a4823c0950f4fa93f7
- https://github.com/python-zeroconf/python-zeroconf
- https://pypi.org/project/zeroconf
- https://github.com/advisories/GHSA-9663-mqmp-p9mm
- https://nvd.nist.gov/vuln/detail/CVE-2026-48045
- 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
- 11.06.2026
- Updated
- 11.10.2026 14:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-3435 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-9663-mqmp-p9mm - 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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