C ares: Prior to 1.34.7, ares_dns_parse() trusts the attacker-controlled ANCOUNT, NSCOUNT, and ARCOUNT fields before confirming that the DNS response… (CVE-2026-69186)
c-ares versions prior to 1.34.7 contain a vulnerability in the ares_dns_parse() function where attacker-controlled DNS response fields (ANCOUNT, NSCOUNT, ARCOUNT) are trusted before verifying the response length. This can lead to excessive heap memory allocation for small messages, causing resource exhaustion and potential denial of service in name resolution. The issue does not cause memory corruption or information disclosure and is fixed in version 1.34.7.
AI Analysis
Technical Summary
The asynchronous resolver library c-ares has a vulnerability in versions before 1.34.7 where the ares_dns_parse() function trusts the ANCOUNT, NSCOUNT, and ARCOUNT fields in DNS responses without confirming the response contains enough bytes for the claimed records. Because process_answer() parses the response before validating the transaction ID and question, a malicious DNS response can cause disproportionate heap memory allocation via ares_dns_record_rr_prealloc() and ares_array_set_size(). Repeated exploitation can degrade or deny DNS resolution service. This vulnerability is addressed in c-ares version 1.34.7.
Potential Impact
An attacker can send malicious DNS responses that cause the vulnerable c-ares library to allocate excessive heap memory repeatedly, leading to degraded performance or denial of service of name resolution. There is no memory corruption or information disclosure associated with this vulnerability.
Mitigation Recommendations
Upgrade to c-ares version 1.34.7 or later, where this issue is fixed. No other mitigation is indicated by the vendor advisory.
C ares: Prior to 1.34.7, ares_dns_parse() trusts the attacker-controlled ANCOUNT, NSCOUNT, and ARCOUNT fields before confirming that the DNS response… (CVE-2026-69186)
Description
c-ares versions prior to 1.34.7 contain a vulnerability in the ares_dns_parse() function where attacker-controlled DNS response fields (ANCOUNT, NSCOUNT, ARCOUNT) are trusted before verifying the response length. This can lead to excessive heap memory allocation for small messages, causing resource exhaustion and potential denial of service in name resolution. The issue does not cause memory corruption or information disclosure and is fixed in version 1.34.7.
CVSS v3.1
Score 5.3medium
Affected software
pkg:deb/ubuntu/c-ares?arch=source&distro=esm-infra/xenialpkg:deb/ubuntu/c-ares?arch=source&distro=esm-infra/bionicpkg:deb/ubuntu/c-ares?arch=source&distro=focalpkg:deb/ubuntu/c-ares?arch=source&distro=jammypkg:deb/ubuntu/c-ares?arch=source&distro=noblepkg:deb/ubuntu/c-ares?arch=source&distro=resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The asynchronous resolver library c-ares has a vulnerability in versions before 1.34.7 where the ares_dns_parse() function trusts the ANCOUNT, NSCOUNT, and ARCOUNT fields in DNS responses without confirming the response contains enough bytes for the claimed records. Because process_answer() parses the response before validating the transaction ID and question, a malicious DNS response can cause disproportionate heap memory allocation via ares_dns_record_rr_prealloc() and ares_array_set_size(). Repeated exploitation can degrade or deny DNS resolution service. This vulnerability is addressed in c-ares version 1.34.7.
Potential Impact
An attacker can send malicious DNS responses that cause the vulnerable c-ares library to allocate excessive heap memory repeatedly, leading to degraded performance or denial of service of name resolution. There is no memory corruption or information disclosure associated with this vulnerability.
Mitigation Recommendations
Upgrade to c-ares version 1.34.7 or later, where this issue is fixed. No other mitigation is indicated by the vendor advisory.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-69186
- Osv Schema Version
- 1.7.0
- Ecosystems
- ["Ubuntu:Pro:16.04:LTS","Ubuntu:Pro:18.04:LTS","Ubuntu:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:26.04:LTS"]
- Cvss Version
- 3.1
Threat ID: 6ab4be55f7a7c54106f0aa40
Added to database: 09/24/2026, 06:08:21 UTC
Last enriched: 09/24/2026, 06:46:37 UTC
Last updated: 09/25/2026, 01:47:44 UTC
Views: 4
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