Use-after-free in c-ares - #VU156259
Published: October 20, 2026
Vulnerability identifier: #VU156259
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-416
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service by crashing an application using c-ares.
The vulnerability exists due to use-after-free in c-ares lookup handling when a failed lookup send causes connection shutdown and another pending lookup's callback calls ares_cancel(), releasing the original lookup while it is still in use. A remote attacker can trigger this sequence in an application with multiple lookups in flight to crash the process and cause a denial of service.
Affected software
c-ares
Remediation
Install security update from vendor's website.
c-ares - update to 1.34.9