PYSEC-2026-3435

Vulnerability from pysec - Published: 2026-07-13 15:46 - Updated: 2026-07-13 16:07
VLAI
Details

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

Severity
6.5 (Medium)
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Impacted products
Name purl
zeroconf pkg:pypi/zeroconf
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "zeroconf",
        "purl": "pkg:pypi/zeroconf"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.149.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.100.0",
        "0.101.0",
        "0.102.0",
        "0.103.0",
        "0.104.0",
        "0.105.0",
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        "0.118.1",
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        "0.147.4",
        "0.148.0",
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        "0.149.1",
        "0.149.10",
        "0.149.11",
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        "0.39.4",
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        "0.44.0",
        "0.45.0",
        "0.46.0",
        "0.47.0",
        "0.47.1",
        "0.47.2",
        "0.47.3",
        "0.47.4",
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        "0.49.0",
        "0.50.0",
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        "0.52.0",
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        "0.53.1",
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        "0.56.0",
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        "0.58.1",
        "0.58.2",
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      ]
    }
  ],
  "aliases": [
    "CVE-2026-48045",
    "GHSA-9663-mqmp-p9mm"
  ],
  "details": "### Impact\n\n`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 \u00a718.5). 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.\n\nAny unauthenticated host on the local link (UDP/5353, `224.0.0.251` / `ff02::fb`) can stream byte-distinct TC-flagged mDNS queries \u2014 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).\n\n### Patches\n\nFixed in `zeroconf` 0.149.12 ([PR #1751](https://github.com/python-zeroconf/python-zeroconf/pull/1751)). Upgrade to `\u003e= 0.149.12`.\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 #1751](https://github.com/python-zeroconf/python-zeroconf/pull/1751), fix\n- [RFC 6762 \u00a718.5](https://www.rfc-editor.org/rfc/rfc6762#section-18.5), [CWE-400](https://cwe.mitre.org/data/definitions/400.html)",
  "id": "PYSEC-2026-3435",
  "modified": "2026-07-13T16:07:36.645444Z",
  "published": "2026-07-13T15:46:16.573699Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-9663-mqmp-p9mm"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/pull/1751"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/commit/b22c8ff19c66c68907d220a4823c0950f4fa93f7"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/python-zeroconf/python-zeroconf"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/zeroconf"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-9663-mqmp-p9mm"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-48045"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "python-zeroconf: Unbounded TC-deferred queue allows LAN-local memory exhaustion via spoofed-source flood"
}



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