Use-after-free in c-ares - CVE-2026-33630
Published: July 7, 2026
Vulnerability identifier: #VU137036
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-33630
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.
The vulnerability exists due to use-after-free in c-ares query-completion handling for ares_getaddrinfo() when processing crafted DNS responses over TCP. A remote attacker can send crafted DNS responses that trigger re-entrant completion handling to cause a denial of service.
An attacker can force the client to retry over TCP by setting the truncation bit in a UDP response, and the issue was observed when a malicious or on-path DNS server returned a FORMERR response without an OPT record, followed by a second response with the same query id and a connection reset.
Affected software
c-ares
Fedora
c-ares
Fedora
c-ares
How to mitigate CVE-2026-33630
Install security update from vendor's website.
c-ares - update to 1.34.7
c-ares - addressed in versions 1.34.7-1.fc43, 1.34.7-1.fc44, 1.34.8-1.fc43
c-ares - addressed in versions 1.34.7-1.fc43, 1.34.7-1.fc44, 1.34.8-1.fc43