pycares has a Use-After-Free Vulnerability

Exploitation

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

CVSS

not scored

EPSS

• CVE-2025-48945: 0.48% estimated exploitation activity in the next 30 days; percentile 41.78 (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.

Summary pycares is vulnerable to a use-after-free condition that occurs when a Channel object is garbage collected while DNS queries are still pending. This results in a fatal Python error and interpreter crash. Details Root Cause The vulnerability stems from improper handling of callback references when the Channel object is destroyed: 1. When a DNS query is initiated, pycares stores a callback reference using ffi.newhandle() 2. If the Channel object is garbage collected while queries are pending, the callback references become invalid 3. When c-ares attempts to invoke the callback, it accesses freed memory, causing a fatal error This issue was much more likely to occur when using eventthread=True but could happen without it under the right circumstances. Technical Details The core issue is a race condition between Python's garbage collector and c-ares's callback execution: 1. When del is called from within a c-ares callback context, we cannot immediately call aresdestroy() because…

Published by the source

16 Jun 2025, 16:09 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:32 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-5qpg-rh4j-qp35

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-5qpg-rh4j-qp35

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# Patch Next advisory brief: CVE-2025-48945

Advisory: pycares has a Use-After-Free Vulnerability
IDs: CVE-2025-48945, GHSA-5qpg-rh4j-qp35
Record: https://patchnext.com/advisories/cve-2025-48945 (revision 2, source checked 26 Oct 2026, 13:32 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pycares 4.9.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pycares: affected <= 4.8.0; fixed in 4.9.0

## Suggested inspection (read-only)
- `python -m pip show pycares`: 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 pycares.
- 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-5qpg-rh4j-qp35 (OSV record GHSA-5qpg-rh4j-qp35 lists affected ranges: PyPI pycares >=0 <4.9.0 (fixed))
- Verified: https://github.com/advisories/GHSA-5qpg-rh4j-qp35 (GitHub-reviewed advisory GHSA-5qpg-rh4j-qp35 lists affected ranges: PyPI pycares >=0 <=4.8.0)

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