CVE-2026-44608
MediumCVSS 5.9Exploitation Probability (EPSS)
Low risk17th percentile - higher than 17% of all known CVEs
Summary
NLnet Labs Unbound from version 1.14.0 up to 1.25.0 has a locking inconsistency vulnerability that under certain conditions (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) can lead to heap use-after-free and crash. An attacker can exploit if conditions are met. Unbound 1.25.1 contains a fix.
Risk Assessment
The vulnerability can cause DNS server crashes, leading to network service disruptions.
Recommendation
Upgrade Unbound to version 1.25.1 or later, which includes a fix for the locking code.
Original NVD description (English source)
NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with a fix to the locking code.