PYSEC-2026-3436

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

Impact

DNSIncoming._decode_labels_at_offset recurses once per DNS-name compression pointer (RFC 1035 §4.1.4). Pointer cycles and label counts were capped, but the chain length of unique forward pointers was not. A single ~3 kB mDNS packet carrying ~1500 chained pointers drives the recursion past CPython's default limit, and RecursionError was not listed in DECODE_EXCEPTIONS, so it escaped DNSIncoming.__init__ and was logged by asyncio's default exception handler.

Any unauthenticated host on the local link (UDP/5353, 224.0.0.251 / ff02::fb) can degrade the mDNS listener; that includes a guest on the same Wi-Fi, a compromised IoT device, or a container on a shared bridge. Replaying at a few hertz produces sustained CPU burn and log flooding, and mDNS-dependent features (HomeKit, Chromecast/Matter, AirPlay, printers) degrade while the attack is in flight.

Patches

Fixed in zeroconf 0.149.5 (PR #1719). Upgrade to >= 0.149.5.

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": "0.149.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.100.0",
        "0.101.0",
        "0.102.0",
        "0.103.0",
        "0.104.0",
        "0.105.0",
        "0.106.0",
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        "0.118.1",
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        "0.147.1",
        "0.147.2",
        "0.147.3",
        "0.147.4",
        "0.148.0",
        "0.149.0",
        "0.149.1",
        "0.149.2",
        "0.149.3",
        "0.149.4",
        "0.15",
        "0.15.1",
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        "0.17.1",
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        "0.24.1",
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        "0.39.2",
        "0.39.3",
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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",
        "0.48.0",
        "0.49.0",
        "0.50.0",
        "0.51.0",
        "0.52.0",
        "0.53.0",
        "0.53.1",
        "0.54.0",
        "0.55.0",
        "0.56.0",
        "0.57.0",
        "0.58.0",
        "0.58.1",
        "0.58.2",
        "0.59.0",
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        "0.61.0",
        "0.62.0",
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        "0.64.0",
        "0.64.1",
        "0.65.0",
        "0.66.0",
        "0.67.0",
        "0.68.0",
        "0.68.1",
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        "0.71.0",
        "0.71.1",
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        "0.71.5",
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        "0.72.1",
        "0.72.2",
        "0.72.3",
        "0.73.0",
        "0.74.0",
        "0.75.0",
        "0.76.0",
        "0.77.0",
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        "0.80.0",
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        "0.82.0",
        "0.82.1",
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        "0.83.1",
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        "0.85.0",
        "0.86.0",
        "0.87.0",
        "0.88.0",
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      ]
    }
  ],
  "aliases": [
    "CVE-2026-47180",
    "GHSA-9pgc-3ccv-5297"
  ],
  "details": "### Impact\n\n`DNSIncoming._decode_labels_at_offset` recurses once per DNS-name compression pointer (RFC 1035 \u00a74.1.4). Pointer cycles and label counts were capped, but the chain length of unique forward pointers was not. A single ~3 kB mDNS packet carrying ~1500 chained pointers drives the recursion past CPython\u0027s default limit, and `RecursionError` was not listed in `DECODE_EXCEPTIONS`, so it escaped `DNSIncoming.__init__` and was logged by asyncio\u0027s default exception handler.\n\nAny unauthenticated host on the local link (UDP/5353, `224.0.0.251` / `ff02::fb`) can degrade the mDNS listener; that includes a guest on the same Wi-Fi, a compromised IoT device, or a container on a shared bridge. Replaying at a few hertz produces sustained CPU burn and log flooding, and mDNS-dependent features (HomeKit, Chromecast/Matter, AirPlay, printers) degrade while the attack is in flight.\n\n### Patches\nFixed in `zeroconf` 0.149.5 ([PR #1719](https://github.com/python-zeroconf/python-zeroconf/pull/1719)).\nUpgrade to `\u003e= 0.149.5`.\n\n### Workarounds\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- [PR #1719](https://github.com/python-zeroconf/python-zeroconf/pull/1719), fix\n- [Issue #1713](https://github.com/python-zeroconf/python-zeroconf/issues/1713), public tracking issue\n- [RFC 1035 \u00a74.1.4](https://www.rfc-editor.org/rfc/rfc1035#section-4.1.4), [RFC 6762](https://www.rfc-editor.org/rfc/rfc6762), [CWE-674](https://cwe.mitre.org/data/definitions/674.html)",
  "id": "PYSEC-2026-3436",
  "modified": "2026-07-13T16:07:36.783034Z",
  "published": "2026-07-13T15:19:14.415629Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-9pgc-3ccv-5297"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/issues/1713"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-zeroconf/python-zeroconf/pull/1719"
    },
    {
      "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-9pgc-3ccv-5297"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-47180"
    }
  ],
  "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 recursion in DNS compression-pointer decoder that allows LAN-local denial of service"
}



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Detection rules are retrieved from Rulezet.