Use-after-free in Unbound - CVE-2026-52863
Published: July 23, 2026
Vulnerability identifier: #VU139226
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-2026-52863
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 memory corruption.
The vulnerability exists due to memory corruption in the view name handling for subqueries when processing queries that combine respip or rpz with a module that can attach subqueries under pressure. A remote attacker can send queries that trigger subquery processing and query jostling to cause memory corruption.
Exploitation requires Unbound to be configured with access-control-view together with respip or rpz and a module such as dns64, subnetcache, or respip CNAME redirection, and the issue occurs when slow queries are dropped under pressure.
How to mitigate CVE-2026-52863
Install security update from vendor's website.