CVE-2026-42534 Affecting unbound-debugsource package, versions <0:1.17.1-1.amzn2023.0.12


Severity

Recommended
high

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
0.05% (15th percentile)

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  • Snyk IDSNYK-AMZN2023-UNBOUNDDEBUGSOURCE-16887744
  • published27 May 2026
  • disclosed20 May 2026

Introduced: 20 May 2026

NewCVE-2026-42534  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 unbound-debugsource to version 0:1.17.1-1.amzn2023.0.12 or higher.
This issue was patched in ALAS2023-2026-1756.

NVD Description

Note: Versions mentioned in the description apply only to the upstream unbound-debugsource package and not the unbound-debugsource package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.

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 Base Scores

version 3.1