Ubuntu released a security advisory targeting several dangerous flaws in Dnsmasq across multiple active and legacy distribution branches. Malicious actors could leverage these memory handling errors and missing validation routines to crash systems or execute arbitrary code remotely. The document outlines specific package version upgrades required to patch each identified vulnerability for every supported release. Administrators can usually resolve the issues through a routine system update, though users on older releases must maintain an active Ubuntu Pro subscription to download the corrected files.

[USN-8268-1] Dnsmasq vulnerabilities

[USN-8268-1] Dnsmasq vulnerabilities

==========================================================================
Ubuntu Security Notice USN-8268-1
May 12, 2026

dnsmasq vulnerabilities
==========================================================================

A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 26.04 LTS
- Ubuntu 25.10
- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS
- Ubuntu 14.04 LTS

Summary:

Several security issues were fixed in Dnsmasq.

Software Description:
- dnsmasq: Small caching DNS proxy and DHCP/TFTP server

Details:

Andrew S. Fasano, Royce M, and Hugo Martinez Ray discovered that Dnsmasq
did not allocate the necessary space to store domain names in some
contexts. An attacker could possibly use this issue to write
out-of-bounds, and could cause a denial of service or execute arbitrary
code. (CVE-2026-2291)

Royce M discovered that Dnsmasq could loop infinitely due to erroneously
missing the window header. An attacker could possibly use this issue to
cause a denial of service. This issue only affected Ubuntu 16.04 LTS,
Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS,
Ubuntu 25.10, and Ubuntu 26.04 LTS. (CVE-2026-4890)

Royce M discovered that a maliciously crafted packet could cause Dnsmasq
to report a negative length. An attacker could possibly use this issue
to cause a denial of service. This issue only affected Ubuntu 16.04 LTS,
Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS,
Ubuntu 25.10, and Ubuntu 26.04 LTS. (CVE-2026-4891)

Royce M and Asim Viladi Oglu Manizada discovered that certain
configurations of Dnsmasq could write over the DHCPv6 CLID buffer within
a privileged helper. An attacker could possibly use this issue to cause
a denial of service or execute arbitrary code. (CVE-2026-4892)

Royce M discovered that certain configurations of Dnsmasq could bypass
internal bounds checks. An attacker could possibly use this issue to
permit malformed packets, and could cause a denial of service.
(CVE-2026-4893)

Hugo Martinez discovered that Dnsmasq did not check the rdlen element of
a record. An attacker could possibly use this issue to cause a denial of
service. This issue only affected Ubuntu 16.04 LTS, Ubuntu 18.04 LTS,
Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 25.10, and
Ubuntu 26.04 LTS. (CVE-2026-5172)

Update instructions:

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

Ubuntu 26.04 LTS
dnsmasq 2.92-1ubuntu0.2

Ubuntu 25.10
dnsmasq 2.91-1ubuntu0.2

Ubuntu 24.04 LTS
dnsmasq 2.90-2ubuntu0.3

Ubuntu 22.04 LTS
dnsmasq 2.90-0ubuntu0.22.04.3

Ubuntu 20.04 LTS
dnsmasq 2.90-0ubuntu0.20.04.1+esm2
Available with Ubuntu Pro

Ubuntu 18.04 LTS
dnsmasq 2.90-0ubuntu0.18.04.1+esm3
Available with Ubuntu Pro

Ubuntu 16.04 LTS
dnsmasq 2.90-0ubuntu0.16.04.1+esm3
Available with Ubuntu Pro

Ubuntu 14.04 LTS
dnsmasq 2.68-1ubuntu0.2+esm5
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-8268-1
CVE-2026-2291, CVE-2026-4890, CVE-2026-4891, CVE-2026-4892,
CVE-2026-4893, CVE-2026-5172

Package Information:
https://launchpad.net/ubuntu/+source/dnsmasq/2.92-1ubuntu0.2
https://launchpad.net/ubuntu/+source/dnsmasq/2.91-1ubuntu0.2
https://launchpad.net/ubuntu/+source/dnsmasq/2.90-2ubuntu0.3
https://launchpad.net/ubuntu/+source/dnsmasq/2.90-0ubuntu0.22.04.3