Vulnerability · Published Sep 18, 2026 · Assigned by GitHub_M
CVE-2026-69186c-ares: Memory-amplification denial of service via unvalidated DNS header record counts
Medium 5.3
In plain English
A medium-severity uncontrolled resource consumption in c-ares from c-ares. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
c-ares is an asynchronous resolver library. Prior to 1.34.7, ares_dns_parse() trusts the attacker-controlled ANCOUNT, NSCOUNT, and ARCOUNT fields before confirming that the DNS response contains enough bytes for the claimed records. Because process_answer() invokes parsing before transaction ID and question validation, a malicious DNS response can cause ares_dns_record_rr_prealloc() and ares_array_set_size() to reserve disproportionate heap memory for a tiny message. Repeated responses create large allocation and release cycles that can degrade or deny name resolution, without causing memory corruption or information disclosure. This issue is fixed in version 1.34.7.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | c-ares | no fix listed | DEBIAN-CVE-2026-69186 |
| Debian:14 | c-ares | 1.34.7-1 | DEBIAN-CVE-2026-69186 |
| Ubuntu:22.04:LTS | c-ares | 1.18.1-1ubuntu0.22.04.4 | USN-8951-1 |
| Ubuntu:24.04:LTS | c-ares | 1.27.0-1.0ubuntu1.1 | USN-8951-1 |
| Ubuntu:24.04:LTS | c-ares | 1.27.0-1.0ubuntu1.1 | UBUNTU-CVE-2026-69186 |
| Ubuntu:26.04:LTS | c-ares | 1.34.6-1ubuntu0.2 | USN-8951-1 |
| Ubuntu:26.04:LTS | c-ares | 1.34.6-1ubuntu0.2 | UBUNTU-CVE-2026-69186 |
Affected products (as reported)
Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
References
- https://github.com/c-ares/c-ares/security/advisories/GHSA-jv8r-gqr9-68wj x_refsource_CONFIRM
- https://github.com/c-ares/c-ares/pull/1134 x_refsource_MISC
- https://github.com/c-ares/c-ares/commit/e47c203f91cd8b749c8736bc18d75a31ffdec8f4 x_refsource_MISC
- https://github.com/c-ares/c-ares/commit/eaded4cb200b2a5f8d73f11021ff7c8d6968aaab x_refsource_MISC
- https://github.com/c-ares/c-ares/releases/tag/v1.34.7 x_refsource_MISC