SB2026111372 - Debian update for c-ares
Published: November 13, 2026
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 4 vulnerabilities.
1) Use-after-free (CVE-ID: CVE-2025-62408)
CWE-ID: CWE-416 - Use After Free
CVSSv4: 6 [CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to perform a denial of service attack.
The vulnerability exists due to a use-after-free error within the read_answer() function when process_answer() terminates a query such as after maximum attempts. A remote attacker can perform a denial of service attack.
Note, the vulnerability exists due to an incomplete fix for #VU107155 (CVE-2025-31498).
2) Use-after-free (CVE-ID: CVE-2026-33630)
CWE-ID: CWE-416 - Use After Free
CVSSv4: 8.7 [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]
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.
3) Inefficient Algorithmic Complexity (CVE-ID: CVE-2026-69184)
CWE-ID: CWE-407 - Inefficient Algorithmic Complexity
CVSSv4: 8.7 [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]
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.
4) Resource exhaustion (CVE-ID: CVE-2026-69186)
CWE-ID: CWE-400 - Resource exhaustion
CVSSv4: 6.9 [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]
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.
Remediation
Install update from vendor's website.