GnuTLS SAN Size ForkCheck Bypass
CVE-2026-42013 Published on May 26, 2026

Gnutls: gnutls: certificate validation bypass due to oversized subject alternative name
A flaw was found in gnutls. When validating certificates, an oversized Subject Alternative Name (SAN) could cause the validation process to incorrectly fall back to checking the Common Name (CN) field. This could allow a remote attacker to bypass proper certificate validation, potentially leading to spoofing or man-in-the-middle attacks.

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Vulnerability Analysis

CVE-2026-42013 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality, a high impact on integrity, and no impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
LOW
Integrity Impact:
HIGH
Availability Impact:
NONE

Timeline

Reported to Red Hat.

Made public.

Weakness Type

Improper Certificate Validation

The software does not validate, or incorrectly validates, a certificate. When a certificate is invalid or malicious, it might allow an attacker to spoof a trusted entity by interfering in the communication path between the host and client. The software might connect to a malicious host while believing it is a trusted host, or the software might be deceived into accepting spoofed data that appears to originate from a trusted host.


Products Associated with CVE-2026-42013

You can be notified by email with stack.watch whenever vulnerabilities like CVE-2026-42013 are published in these products:

Canonical Ubuntu Linux
 
Red Hat Enterprise Linux (RHEL)
 
Red Hat Hummingbird
 
Red Hat Openshift
 
Red Hat Enterprise Linux Eus
 
Red Hat Rhui
 
Red Hat Discovery
 
Red Hat Rhel Eus
 
Red Hat Rhel Aus
 
Red Hat Rhel Eus Long Life
 
Red Hat Rhel E4s
 
Red Hat Rhel Tus
 

Affected Versions

Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 10.0 Extended Update Support: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support: Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support: Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On: Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On: Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support: Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support: Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On: Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On: Red Hat Enterprise Linux 8.8 Telecommunications Update Service: Red Hat Enterprise Linux 8.8 Telecommunications Update Service: Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions: Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions: Red Hat Enterprise Linux 9.6 Extended Update Support: Red Hat Discovery 2: Red Hat Discovery 2: Red Hat Update Infrastructure 5: Red Hat Update Infrastructure 5: Red Hat Update Infrastructure 5: Red Hat Update Infrastructure 5: Red Hat Enterprise Linux 6: Red Hat Enterprise Linux 7: Red Hat Hardened Images: Red Hat OpenShift Container Platform 4:

Exploit Probability

EPSS
0.40%
Percentile
31.69%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.