What’s Vulnerable › Vulnerabilities

CVE-2026-69186: c-ares: Memory-amplification denial of service via unvalidated DNS header record counts

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-18 · updated 2026-09-23
• Weakness: CWE-400

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 products

• c-ares: before 1.34.7

References

• https://github.com/c-ares/c-ares/commit/e47c203f91cd8b749c8736bc18d75a31ffdec8f4
• https://github.com/c-ares/c-ares/commit/eaded4cb200b2a5f8d73f11021ff7c8d6968aaab
• https://github.com/c-ares/c-ares/pull/1134
• https://github.com/c-ares/c-ares/releases/tag/v1.34.7
• https://github.com/c-ares/c-ares/security/advisories/GHSA-jv8r-gqr9-68wj
• https://github.com/c-ares/c-ares/security/advisories/GHSA-jv8r-gqr9-68wj

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