CVE-2026-69186: DoS (CVSS 5.3)

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.

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CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS — Exploit Prediction

0.0052

Probability of exploitation

0.43%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-400 Uncontrolled Resource Consumption

References

Other 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

Frequently Asked Questions

What is CVE-2026-69186? +

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. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-69186? +

CVE-2026-69186 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0052, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-69186? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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