Ubuntu 26.04 Dnsmasq Critical DoS Risk Advisory USN-8268-1 CVE-2026-2291

ubuntu

May 13, 2026

Several security issues were fixed in Dnsmasq.

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...

Read the Full Advisory

Topics Covered

security advisory DoS arbitrary code execution Ubuntu out-of-bounds dnsmasq

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.