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CVE-2026-69186

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

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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.

CVSS 5.3 · Medium · EPSS 0.5% · Fix available

Published
Updated

Stack: system

Affected products and versions

  • c-ares

    Versions
    • < 1.34.7: Affected

    No fix published

  • c-ares Debian:13

    Versions
    • 1.34.5-1
    • 1.34.5-1+deb13u1
    • 1.34.6-1
    • 1.34.7-1
    • 1.34.8-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • c-ares Debian:14

    Versions
    • 1.34.5-1
    • 1.34.6-1
    Affected ranges
    • ECOSYSTEM: < 1.34.7-1

    Update to 1.34.7-1

  • c-ares Ubuntu:24.04:LTS

    Versions
    • 1.19.1-3
    • 1.20.1-1
    • 1.26.0-1
    • 1.27.0-1
    • 1.27.0-1.0ubuntu1
    Affected ranges
    • ECOSYSTEM: < 1.27.0-1.0ubuntu1.1

    Update to 1.27.0-1.0ubuntu1.1

  • c-ares Ubuntu:26.04:LTS

    Versions
    • 1.34.5-1
    • 1.34.6-1
    • 1.34.6-1ubuntu0.1
    Affected ranges
    • ECOSYSTEM: < 1.34.6-1ubuntu0.2

    Update to 1.34.6-1ubuntu0.2

Original sources

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