Input validation error in Unbound - CVE-2026-32665
Published: July 23, 2026
Vulnerability identifier: #VU139240
CSH Severity: Medium
CVSS v4.0: 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/E:U/U:Green
CVE-ID: CVE-2026-32665
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: NLnet Labs
Affected software:
Unbound
Unbound
Detailed vulnerability description
The vulnerability allows a remote attacker to cause a denial of service for new DoQ clients.
The vulnerability exists due to improper input validation in the downstream DNS-over-QUIC implementation when processing client-provided stream length values on new QUIC connections. A remote attacker can send specially crafted QUIC streams with large declared lengths to cause a denial of service for new DoQ clients.
The issue affects the first two bidirectional streams on a new QUIC connection and requires Unbound to be built with DoQ support and configured to listen on a quic-port.
How to mitigate CVE-2026-32665
Install security update from vendor's website.