CVE-2026-44608
CVE-2026-44608 is a medium-severity vulnerability in Nlnetlabs Unbound with a CVSS 3.x base score of 5.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-413.
Key facts
- Severity: Medium (CVSS 3.x base score 5.9)
- CVSS v4: 4.6
- EPSS exploit prediction: 0% (17th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-31087
- Weakness: CWE-413
- Affected product: Nlnetlabs Unbound
- Published:
- Last modified:
Description
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.
Frequently asked questions
- What is CVE-2026-44608?
- 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.
- How severe is CVE-2026-44608?
- CVE-2026-44608 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
- Is CVE-2026-44608 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (17th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-44608?
- CVE-2026-44608 affects Nlnetlabs Unbound. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-44608?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-44608 have an EU (EUVD) identifier?
- Yes. CVE-2026-44608 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-31087.
- When was CVE-2026-44608 published?
- CVE-2026-44608 was published on 2026-05-20 and last updated on 2026-06-17.
References
Affected products (1)
- cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*
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