USN-8268-1: Dnsmasq vulnerabilities

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)