๐Ÿ›ก๏ธ CVE-2026-42959
๐ŸŸ  CVSS 7.5 โ€” High โœ… No Known Exploit CWE-824 NVD
7.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets.

Details

Severity HIGH
CVSS Score 7.5
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-824
Public Exploit โœ… No
Source NVD
Published 2026-05-20
Updated 2026-06-02
Modified 2026-05-20
Fix URL N/A

Affected Packages

Software From version Fixed in
unbound โ€” 1.25.1

References

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