Input validation error in NSD - CVE-2026-19401
Published: August 26, 2026
Vulnerability identifier: #VU145738
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-2026-19401
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to improper input validation in the NSD server child process when handling specially crafted UDP DNS queries with multiple DNS Cookie options. A remote attacker can send a specially crafted query to cause a denial of service.
Only debugging or non-release builds are vulnerable, and sustained exploitation can severely hamper service or deny DNS service.
Affected software
NSD
Fedora
nsd
Fedora
nsd
How to mitigate CVE-2026-19401
Install security update from vendor's website.
NSD - update to 4.15.1
nsd - addressed in versions 4.15.1-1.el9, 4.15.1-1.el10_2, 4.15.1-1.el10_3, 4.15.1-1.el10_4, 4.15.1-1.fc43, 4.15.1-1.fc44, 4.15.1-1.fc45
nsd - addressed in versions 4.15.1-1.el9, 4.15.1-1.el10_2, 4.15.1-1.el10_3, 4.15.1-1.el10_4, 4.15.1-1.fc43, 4.15.1-1.fc44, 4.15.1-1.fc45