SB2026070774 - Multiple vulnerabilities in c-ares

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Main Vulnerability Database SB2026070774

SB2026070774 - Multiple vulnerabilities in c-ares

Published: July 7, 2026

Security Bulletin ID SB2026070774
CSH Severity
Medium
Patch available
YES
Number of vulnerabilities 3
Exploitation vector Remote access
Highest impact Denial of service

Breakdown by Severity

Medium 100%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 3 vulnerabilities.


1) Inefficient Algorithmic Complexity (CVE-ID: N/A)

CWE-ID: CWE-407 - Inefficient Algorithmic Complexity

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to inefficient algorithmic complexity in ares_dns_name_parse() when parsing crafted DNS responses with unbounded compression pointer chains. A remote attacker can send a specially crafted DNS response to cause a denial of service.

Because c-ares runs on a single-threaded event loop, parsing a crafted response can stall all resolution for the duration.


2) Resource exhaustion (CVE-ID: N/A)

CWE-ID: CWE-400 - Resource exhaustion

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to uncontrolled resource consumption in the DNS response parser when parsing DNS responses. A remote attacker can send a specially crafted DNS response with forged header record counts to cause a denial of service.

The issue is triggered before transaction-ID validation or question matching, and sustained exploitation is required to produce allocator pressure that degrades availability.


3) Use-after-free (CVE-ID: CVE-2026-33630)

CWE-ID: CWE-416 - Use After Free

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to use-after-free in c-ares query-completion handling for ares_getaddrinfo() when processing crafted DNS responses over TCP. A remote attacker can send crafted DNS responses that trigger re-entrant completion handling to cause a denial of service.

An attacker can force the client to retry over TCP by setting the truncation bit in a UDP response, and the issue was observed when a malicious or on-path DNS server returned a FORMERR response without an OPT record, followed by a second response with the same query id and a connection reset.


Remediation

Install update from vendor's website.

References