Input validation error in Dnsmasq - CVE-2026-4893

Vulnerability identifier: #VU131142

CSH Severity: Medium

CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-4893

CWE-ID: CWE-20

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to bypass client subnet source validation.

The vulnerability exists due to improper input validation in check_source() handling in process_reply() when processing DNS replies with the --add-subnet feature enabled. A remote attacker can send a specially crafted DNS reply to bypass client subnet source validation.

Only configurations with --add-subnet enabled are vulnerable.

Dnsmasq
Gentoo Linux
Debian Linux
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for ARM 64
Anolis OS
Red Hat Enterprise Linux Server - AUS
Red Hat Enterprise Linux for x86_64 - Extended Update Support
Red Hat Enterprise Linux for IBM z Systems - Extended Update Support
Red Hat Enterprise Linux for Power, little endian - Extended Update Support
Red Hat Enterprise Linux for ARM 64 - Extended Update Support
Ubuntu
openEuler
Red Hat Enterprise Linux Server for Power LE - Update Services for SAP Solutions
net-dns/dnsmasq
dnsmasq (Ubuntu package)
dnsmasq-utils
dnsmasq
dnsmasq (Red Hat package)
dnsmasq-debuginfo
dnsmasq-help
dnsmasq-debugsource
dnsmasq-langpack
dnsmasq-doc
dnsmasq (Debian package)

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-utils - addressed in versions 2.79-36, 2.90-2
dnsmasq - addressed in versions 2.79-36, 2.90-2
dnsmasq (Red Hat package) - addressed in versions 2.79-36.el8_10, 2.85-17.el9_6.1, 2.85-18.el9_8.1
dnsmasq-debuginfo - addressed in versions 2.82-21, 2.86-15, 2.90-8, 2.90-9
dnsmasq-help - addressed in versions 2.82-21, 2.86-15, 2.90-8, 2.90-9
dnsmasq-debugsource - addressed in versions 2.82-21, 2.86-15, 2.90-8, 2.90-9
dnsmasq - addressed in versions 2.82-21, 2.86-15, 2.90-8, 2.90-9
dnsmasq-langpack - update to 2.90-2
dnsmasq-doc - update to 2.90-2
dnsmasq (Debian package) - addressed in versions 2.90-4~deb12u2, 2.91-1+deb13u1

• https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2026q2/018471.html
• https://thekelleys.org.uk/dnsmasq/CVE/CVE-2026-4893.diff

• Multiple vulnerabilities in Dnsmasq
• Debian update for dnsmasq
• Ubuntu update for dnsmasq
• Red Hat Enterprise Linux 9 update for dnsmasq
• Anolis OS update for dnsmasq
• openEuler 22.03 LTS SP4 update for dnsmasq
• openEuler 20.03 LTS SP4 update for dnsmasq
• openEuler 24.03 LTS SP3 update for dnsmasq
• openEuler 24.03 LTS update for dnsmasq
• Red Hat Enterprise Linux 8 update for dnsmasq
• openEuler 24.03 LTS SP1 update for dnsmasq
• Anolis OS update for dnsmasq
• Red Hat Enterprise Linux 9 update for dnsmasq
• Gentoo update for Dnsmasq