Out-of-bounds read in Dnsmasq - CVE-2026-5172

Vulnerability identifier: #VU131141

CSH Severity: Medium

CVSS v4: 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]

CVE-ID: CVE-2026-5172

CWE-ID: CWE-125

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to out-of-bounds read in extract_addresses() when parsing a DNS resource record with a falsified rdlen value. A remote attacker can send a specially crafted DNS packet to cause a denial of service.

The issue occurs because extract_name() can advance the record pointer past the calculated end of the resource record, causing the remaining-length calculation to underflow.

Dnsmasq
Debian Linux
Gentoo Linux
Ubuntu
Anolis OS
openEuler
net-dns/dnsmasq
dnsmasq (Ubuntu package)
dnsmasq-langpack
dnsmasq-doc
dnsmasq-utils
dnsmasq
dnsmasq (Debian package)
dnsmasq-help
dnsmasq-debuginfo
dnsmasq-debugsource

Install security update from vendor's website.

Dnsmasq - update to 2.92
net-dns/dnsmasq - update to 2.66
dnsmasq (Ubuntu package) - addressed in versions 2.68-1ubuntu0.2+esm5, 2.90-0ubuntu0.16.04.1+esm3, 2.90-0ubuntu0.18.04.1+esm3, 2.90-0ubuntu0.20.04.1+esm2, 2.90-0ubuntu0.22.04.3, 2.90-2ubuntu0.3, 2.91-1ubuntu0.2, 2.92-1ubuntu0.2
dnsmasq-langpack - update to 2.90-2
dnsmasq-doc - update to 2.90-2
dnsmasq-utils - update to 2.90-2
dnsmasq - update to 2.90-2
dnsmasq (Debian package) - addressed in versions 2.90-4~deb12u2, 2.91-1+deb13u1
dnsmasq-help - addressed in versions 2.90-8, 2.90-9
dnsmasq - addressed in versions 2.90-8, 2.90-9
dnsmasq-debuginfo - addressed in versions 2.90-8, 2.90-9
dnsmasq-debugsource - addressed in versions 2.90-8, 2.90-9

• https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2026q2/018471.html
• https://thekelleys.org.uk/dnsmasq/CVE/CVE-2026-5172.diff

• Multiple vulnerabilities in Dnsmasq
• Debian update for dnsmasq
• Ubuntu update for dnsmasq
• Anolis OS update for dnsmasq
• openEuler 24.03 LTS SP3 update for dnsmasq
• openEuler 24.03 LTS update for dnsmasq
• openEuler 24.03 LTS SP1 update for dnsmasq
• Gentoo update for Dnsmasq