PYSEC-2026-3439

Vulnerability from pysec - Published: 2026-07-13 15:19 - Updated: 2026-07-13 16:07
VLAI
Details

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

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": "0.149.7"
            }
          ],
          "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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      ]
    }
  ],
  "aliases": [
    "CVE-2026-47184",
    "GHSA-rfg2-pjw2-56x2"
  ],
  "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 \u00a710), 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 \u00a711 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 \u2014 re-multicasting cached records with shifting TTLs \u2014 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 `\u003e= 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 \u00a710](https://www.rfc-editor.org/rfc/rfc6762#section-10), [RFC 6762 \u00a711](https://www.rfc-editor.org/rfc/rfc6762#section-11), [CWE-400](https://cwe.mitre.org/data/definitions/400.html)",
  "id": "PYSEC-2026-3439",
  "modified": "2026-07-13T16:07:37.186351Z",
  "published": "2026-07-13T15:19:14.814605Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-rfg2-pjw2-56x2"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/issues/1715"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/pull/1718"
    },
    {
      "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-rfg2-pjw2-56x2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-47184"
    }
  ],
  "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": "zeroconf has unbounded DNS record cache that allows LAN-local memory exhaustion via multicast flood"
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.