CVE-2026-42534NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the jostle logic that could defeat its purpose and degrade resolution performance.
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NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the jostle logic that could defeat its purpose and degrade resolution performance. Retransmits of the same query could renew the age of slow running queries and not allow the jostle logic to see them as aged and potential targets for replacement with new queries. An adversary who can query a vulnerable Unbound and who can control a domain name server that replies slowly and/or maliciously to Unbound's queries can exploit the vulnerability and degrade the resolution performance of Unbound. When Unbound's 'num-queries-per-thread' reaches its limit, the jostle logic kicks in. When a new query comes in, half of the available queries that are also slow to resolve are candidates for replacement. The vulnerability then happens because duplicate queries that need resolution would skew the aging result by using the timestamp of the latest duplicate query instead of the original one that started the resolution effort. Cache and local data response performance remains unaffected. Coordinated attacks could raise this to a denial of resolution service. Unbound 1.25.1 contains a patch with a fix to attach an initial, non-updatable start time for incoming queries that allow the jostle logic to work as intended.
- CVSS
- 5.3 MEDIUM (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Weakness (CWE)
- CWE-440, CWE-911
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Modified
- Record last updated
- Sep 1, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
nlnetlabs unbound nlnetlabs:unbound | before 1.25.1 | NVD |
References
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42534.txtmitigation, vendor-advisory
- https://access.redhat.com/errata/RHSA-2026:24013
- https://access.redhat.com/errata/RHSA-2026:36320
- https://access.redhat.com/errata/RHSA-2026:36777
- https://access.redhat.com/errata/RHSA-2026:37282
- https://access.redhat.com/security/cve/CVE-2026-42534
- https://bugzilla.redhat.com/show_bug.cgi?id=2480131
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42534.json
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.