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🛡️ CVE-2025-31498 on Ubuntu — c-ares

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

c-ares is an asynchronous resolver library. From 1.32.3 through 1.34.4, there is a use-after-free in read_answers() when process_answer() may re-enqueue a query either due to a DNS Cookie Failure or when the upstream server does not properly support EDNS, or possibly on TCP queries if the remote closed the connection immediately after a response. If there was an issue trying to put that new transaction on the wire, it would close the connection handle, but read_answers() was still expecting the connection handle to be available to possibly dequeue other responses. In theory a remote attacker might be able to trigger this by flooding the target with ICMP UNREACHABLE packets if they also control the upstream nameserver and can return a result with one of those conditions, this has been untested. Otherwise only a local attacker might be able to change system behavior to make send()/write() return a failure condition. This vulnerability is fixed in 1.34.5.

Distribution advisory

This page covers CVE-2025-31498 as tracked by Ubuntu, for the package c-ares. The fix is available in version 1.34.4-2.1ubuntu0.1; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality low, integrity low, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: High — the attacker first has to win a race, learn a secret or otherwise prepare the target.
  • Attack requirements: None — no deployment-specific condition has to hold.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Confidentiality impact: Low — limited, and the attacker does not choose what is affected.
  • Integrity impact: Low — limited, and the attacker does not choose what is affected.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

UBUNTU-CVE-2025-31498 is classified as CWE-416: Use After Free. Memory is used after being released, so its contents may already belong to something else.

Affected software

UBUNTU-CVE-2025-31498 is recorded against 1 package.

  • c-ares (fixed in 1.34.4-2.1ubuntu0.1)

Timeline and source

Published on 8 April 2025 and last revised on 4 February 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

ubuntu.com (Report)
www.cve.org (Report)
github.com (Report)
www.openwall.com (Report)
github.com (Report)
github.com (Report)
ubuntu.com (Advisory)

Other advisories for this package

c-ares has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-416: Use After Free) in other software:

CVE-2025-31498 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity Unknown
CVSS Score N/A
CVSS Vector CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2025-04-08
Updated 2026-08-20
Modified 2026-02-04
Fix URL N/A

Affected Packages

Software From version Fixed in
c-ares — 1.34.4-2.1ubuntu0.1

Similar Threats

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