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Medium, CVSS 4.9amended

zeroconf: Unvalidated rdlength in record payload readers allows LAN-local cache corruption via crafted mDNS packet

CVE-2026-48487GHSA-qc2x-6f54-m6h9

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (zeroconf 0.149.16), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI zeroconf

    Affected
    < 0.149.16
    Fixed in
    0.149.16

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
4.9 · CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U · score source
EPSS
  • CVE-2026-48487: 0.47% estimated exploitation activity in the next 30 days; percentile 40.48 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact readcharacterstring and readstring in src/zeroconf/protocol/incoming.py sliced self.data[self.offset : self.offset + length] and advanced self.offset by the declared length without checking it against self.datalen. Python's slice silently returns fewer bytes when the end index runs past the buffer, so a record whose 16-bit RDLENGTH (RFC 1035 §3.2.1) over-advertised by tens of kilobytes was constructed from a truncated payload, appended to DNSIncoming.answers, and committed to the cache before any later parse failure surfaced. The follow-up readname for the next record then failed, but the corrupt record had already entered the answer list and propagated to DNSCache and ServiceInfo. Any unauthenticated host on the local link (UDP/5353, 224.0.0.251 / ff02::fb) can multicast a single mDNS response carrying a TXT, HINFO, or A/AAAA record that advertises rdlength=65535 and only a handful of real payload bytes; consumers calling ServiceInfo.properties then parse the truncated bytes…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-qc2x-6f54-m6h9

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-qc2x-6f54-m6h9

Agent brief

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# Patch Next advisory brief: CVE-2026-48487

Advisory: zeroconf: Unvalidated rdlength in record payload readers allows LAN-local cache corruption via crafted mDNS packet
IDs: CVE-2026-48487, GHSA-qc2x-6f54-m6h9
Record: https://patchnext.com/advisories/cve-2026-48487 (revision 3, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: zeroconf 0.149.16. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI zeroconf: affected < 0.149.16; fixed in 0.149.16

## 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-qc2x-6f54-m6h9 (OSV record GHSA-qc2x-6f54-m6h9 lists affected ranges: PyPI zeroconf >=0 <0.149.16 (fixed))
- Verified: https://github.com/advisories/GHSA-qc2x-6f54-m6h9 (GitHub-reviewed advisory GHSA-qc2x-6f54-m6h9 lists affected ranges: PyPI zeroconf >=0 <0.149.16)

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