PT-2026-42130 · Nlnet+1 · Unbound+1

Qifan Zhang · Published 2026-05-20 · Updated 2026-05-20 · CVE-2026-42923

Positive Technologies (AI Summary)

CVSS v4.0

6.9

Medium

Base vector

AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/U:Amber

Name of the Vulnerable Software and Affected Versions NLnet Labs Unbound versions prior to 1.25.1

Description A flaw in the DNSSEC validator occurs when the code path used to consult the negative cache for DS records ignores the limit on NSEC3 hash calculations. An attacker controlling a DNSSEC signed zone can exploit this by signing NSEC3 records with high iterations for child delegations and querying the system. This causes the software to perform excessive hash calculations, holding a global lock for the negative cache and blocking other threads. This results in service degradation and can lead to a denial of service through coordinated attacks.

Recommendations Update to version 1.25.1.

Fix

DoS

Weakness Enumeration

CWE-407

Related Identifiers

CVE-2026-42923

USN-8282-1

Affected Products

Ubuntu

Unbound

References · 21

• https://ubuntu.com/security/CVE-2026-41292 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-42923 · Security Note
• https://ubuntu.com/security/CVE-2026-44390 · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-42959 · Vendor Advisory
• https://osv.dev/vulnerability/UBUNTU-CVE-2026-42923 · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-44608 · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-42923 · Vendor Advisory
• https://ubuntu.com/security/notices/USN-8282-1 · Vendor Advisory
• https://osv.dev/vulnerability/USN-8282-1 · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-42960 · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-32792 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2026-42923 · Security Note
• https://ubuntu.com/security/CVE-2026-42534 · Vendor Advisory
• https://nlnetlabs.nl/downloads/unbound/CVE-2026-42923.txt · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-33278 · Vendor Advisory