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[USN-8951-1] c-ares vulnerabilities

Posted on 21 October 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8951-1
October 21, 2026

c-ares vulnerabilities
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 26.04 LTS
- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in c-ares.

Software Description:
- c-ares: library for asynchronous name resolution

Details:

It was discovered that c-ares incorrectly parsed certain SOA replies. A
remote attacker could possibly use this issue to cause c-ares to crash,
resulting in a denial of service. This issue only affected Ubuntu 16.04 LTS
and Ubuntu 18.04 LTS. (CVE-2020-22217)

It was discovered that c-ares incorrectly handled certain sortlist strings.
A remote attacker could possibly use this issue to cause c-ares to crash,
resulting in a denial of service, or execute arbitrary code. This issue
only affected Ubuntu 16.04 LTS. (CVE-2022-4904)

It was discovered that c-ares did not properly limit DNS compression
pointer hops or assembled name lengths when parsing DNS names. A remote
attacker could possibly use this issue to cause c-ares to use excessive
resources, resulting in a denial of service. (CVE-2026-69184)

It was discovered that c-ares did not properly validate record count fields
before allocating memory when parsing DNS responses. A remote attacker
could possibly use this issue to cause c-ares to use excessive resources,
resulting in a denial of service. This issue only affected Ubuntu 24.04 LTS
and Ubuntu 26.04 LTS. (CVE-2026-69186)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 26.04 LTS
libcares2 1.34.6-1ubuntu0.2

Ubuntu 24.04 LTS
libcares2 1.27.0-1.0ubuntu1.1

Ubuntu 22.04 LTS
libc-ares2 1.18.1-1ubuntu0.22.04.4

Ubuntu 20.04 LTS
libc-ares2 1.15.0-1ubuntu0.5+esm1
Available with Ubuntu Pro

Ubuntu 18.04 LTS
libc-ares2 1.14.0-1ubuntu0.2+esm3
Available with Ubuntu Pro

Ubuntu 16.04 LTS
libc-ares2 1.10.0-3ubuntu0.2+esm4
Available with Ubuntu Pro

In general, a standard system update will make all the necessary changes.

References:
https://ubuntu.com/security/notices/USN-8951-1
CVE-2020-22217, CVE-2022-4904, CVE-2026-69184, CVE-2026-69186

Package Information:
https://launchpad.net/ubuntu/+source/c-ares/1.34.6-1ubuntu0.2
https://launchpad.net/ubuntu/+source/c-ares/1.27.0-1.0ubuntu1.1
https://launchpad.net/ubuntu/+source/c-ares/1.18.1-1ubuntu0.22.04.4

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