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National Vulnerability Database

National Vulnerability Database

NVD

National Vulnerability Database
  1. Vulnerabilities

CVE-2026-42534 Detail

Description

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.


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
NVD assessment not yet provided.

Nist CVSS score does not match with CNA score
CNA:  NLnet Labs
CVSS-B 6.9 MEDIUM
Vector:  CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/U:Amber

References to Advisories, Solutions, and Tools

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URL Source(s) Tag(s)
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42534.txt NLnet Labs

Weakness Enumeration

CWE-ID CWE Name Source
CWE-440 Expected Behavior Violation NLnet Labs  

Change History

1 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2026-42534
NVD Published Date:
05/20/2026
NVD Last Modified:
05/20/2026
Source:
NLnet Labs