CVE-2026-42959highCWE-824

CVE-2026-42959: high-severity vulnerability in NLnet Labs Unbound

Crash during DNSSEC validation of malicious content

Published · Updated

Follow this CVE+ Monitor Unbound+ Monitor unbound

E-mail alert when it lands in KEV, gets a public PoC or its score goes up.

21Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 8.7epss 0.8%
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.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/U:Red
Affected products
NLnet Labs · Unbound
Related CVEs — NLnet Labs Unbound

In the same product, most dangerous first.

CVE-2024-1931HIGHDenial of service when trimming EDE text on positive repliesEPSS 2.5%CVE-2022-3204HIGHNRDelegation AttackEPSS 1.6%CVE-2026-33278CRITICALPossible arbitrary code execution during DNSSEC validationEPSS 1.4%CVE-2022-30699—Novel "ghost domain names" attack by updating almost expired delegation informationEPSS 1.2%CVE-2022-30698—Novel "ghost domain names" attack by introducing subdomain delegationsEPSS 1.2%CVE-2026-81642CRITICALHeap buffer overflow and possible Remote Code Execution when digesting DNSKEYEPSS 1.0%