CVE-2026-42923 - Medium Severity Vulnerability
Vulnerable Libraries - src4.0.4, src4.0.4, src4.0.4
src4.0.4
Library home page: https://github.com/MidnightBSD/src.git
Vulnerable Source Files (3)
/contrib/unbound/validator/val_nsec3.h
/contrib/unbound/validator/val_neg.c
/contrib/unbound/validator/val_nsec3.c
src4.0.4
Library home page: https://github.com/MidnightBSD/src.git
Vulnerable Source Files (3)
/contrib/unbound/validator/val_nsec3.h
/contrib/unbound/validator/val_neg.c
/contrib/unbound/validator/val_nsec3.c
src4.0.4
Library home page: https://github.com/MidnightBSD/src.git
Vulnerable Source Files (3)
/contrib/unbound/validator/val_nsec3.h
/contrib/unbound/validator/val_neg.c
/contrib/unbound/validator/val_nsec3.c
Found in HEAD commit: 816463d989cc5839c1cca2efb5bf2503408507fb
Found in base branches: stable/4.0, master
Vulnerability Details
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.
Publish Date: 2026-05-20
URL: CVE-2026-42923
CVSS 3 Score Details (5.3)
Base Score Metrics:
- Exploitability Metrics:
- Attack Vector: Network
- Attack Complexity: Low
- Privileges Required: None
- User Interaction: None
- Scope: Unchanged
- Impact Metrics:
- Confidentiality Impact: None
- Integrity Impact: None
- Availability Impact: Low
For more information on CVSS3 Scores, click here.
Suggested Fix
Type: Upgrade version
Release Date: 2026-05-20
Fix Resolution: https://github.com/NLnetLabs/unbound.git - release-1.25.1
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CVE-2026-42923 - Medium Severity Vulnerability
src4.0.4
Library home page: https://github.com/MidnightBSD/src.git
src4.0.4
Library home page: https://github.com/MidnightBSD/src.git
src4.0.4
Library home page: https://github.com/MidnightBSD/src.git
Found in HEAD commit: 816463d989cc5839c1cca2efb5bf2503408507fb
Found in base branches: stable/4.0, master
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.
Publish Date: 2026-05-20
URL: CVE-2026-42923
Base Score Metrics:
- Exploitability Metrics:
- Attack Vector: Network
- Attack Complexity: Low
- Privileges Required: None
- User Interaction: None
- Scope: Unchanged
- Impact Metrics:
- Confidentiality Impact: None
- Integrity Impact: None
- Availability Impact: Low
For more information on CVSS3 Scores, click here.Type: Upgrade version
Release Date: 2026-05-20
Fix Resolution: https://github.com/NLnetLabs/unbound.git - release-1.25.1
Step up your Open Source Security Game with Mend here