zeroconf has unbounded recursion in DNS compression-pointer decoder that allows LAN-local denial of service

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-47180: 0.37% estimated exploitation activity in the next 30 days; percentile 30.98 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact DNSIncoming.decodelabelsatoffset 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 DECODEEXCEPTIONS, 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.…

Published by the source

29 May 2026, 20:09 UTC

Last modified by the source

13 Jul 2026, 16:43 UTC

Source last checked

26 Oct 2026, 13:41 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-9pgc-3ccv-5297

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-9pgc-3ccv-5297

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# Patch Next advisory brief: CVE-2026-47180

Advisory: zeroconf has unbounded recursion in DNS compression-pointer decoder that allows LAN-local denial of service
IDs: CVE-2026-47180, GHSA-9pgc-3ccv-5297
Record: https://patchnext.com/advisories/cve-2026-47180 (revision 2, source checked 26 Oct 2026, 13:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: zeroconf 0.149.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI zeroconf: affected < 0.149.5; fixed in 0.149.5

## Suggested inspection (read-only)
- `python -m pip show zeroconf`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on zeroconf.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-9pgc-3ccv-5297 (OSV record GHSA-9pgc-3ccv-5297 lists affected ranges: PyPI zeroconf >=0 <0.149.5 (fixed))
- Verified: https://github.com/advisories/GHSA-9pgc-3ccv-5297 (GitHub-reviewed advisory GHSA-9pgc-3ccv-5297 lists affected ranges: PyPI zeroconf >=0 <0.149.5)

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