Off-by-one in Unbound - CVE-2026-44687
Published: July 23, 2026
Vulnerability identifier: #VU139235
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-44687
CWE-ID: CWE-193
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.
The vulnerability exists due to an off-by-one error in harden-below-nxdomain logic when processing queries for the intermediate label between a configured stub or forward zone apex and its DNSSEC parent zone. A remote attacker can send a specially crafted query to cause a denial of service.
The issue can prevent the configured stub or forward upstream from being contacted by causing a DNSSEC-secure NXDOMAIN answer from the public parent to shadow the zone.
How to mitigate CVE-2026-44687
Install security update from vendor's website.