Improper control of a resource through its lifetime in Unbound - CVE-2026-56444
Published: July 23, 2026
Vulnerability identifier: #VU139218
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-2026-56444
CWE-ID: CWE-664
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 improper state management in the serve-expired logic when handling duplicate in-flight queries for a client-controlled slow-on-demand authoritative zone. A remote attacker can issue crafted queries to cause a denial of service.
Only configurations with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' are vulnerable, while the shipped default values make the affected branch unreachable.
How to mitigate CVE-2026-56444
Install security update from vendor's website.