Resource exhaustion in Unbound - CVE-2026-41637
Published: July 23, 2026
Vulnerability identifier: #VU139238
CSH Severity: Low
CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-41637
CWE-ID: CWE-400
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 resource accounting in the DNS-over-QUIC query handling component when processing queries that are terminated by QUIC control frames. A remote attacker can send DNS-over-QUIC queries for names that require resolution and immediately terminate them to cause a denial of service.
Only deployments built with DNS-over-QUIC support and configured to listen on a QUIC port are vulnerable. Exploitation additionally requires access to multiple source IP addresses to bypass the default wait-limit setting.
Affected software
Unbound
Debian Linux
Fedora
unbound
unbound (Debian package)
Debian Linux
Fedora
unbound
unbound (Debian package)
How to mitigate CVE-2026-41637
Install security update from vendor's website.
Unbound - update to 1.25.2
unbound - update to 1.25.2-1.fc43
unbound (Debian package) - update to 1.26.1-0+deb13u1
unbound - update to 1.25.2-1.fc43
unbound (Debian package) - update to 1.26.1-0+deb13u1