Use-after-free in Unbound - CVE-2026-33278
Published: May 20, 2026
Vulnerability identifier: #VU131924
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-33278
CWE-ID: CWE-416
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 and potentially execute arbitrary code.
The vulnerability exists due to use-after-free in Unbound DNSSEC validator when processing validation state for DS sub-queries after deep-copying response messages during NSEC3 computational budget exhaustion. A remote attacker can control a malicious signed zone and query a vulnerable resolver to cause a denial of service and potentially execute arbitrary code.
Exploitation requires control of a malicious signed zone.
How to mitigate CVE-2026-33278
Install security update from vendor's website.