CVE-2026-6450 in wolfSSL
Summary
by MITRE • 06/26/2026
A CRL critical extension bypass exists in ParseCRL_Extensions where critical extensions are not properly enforced, allowing a crafted CRL with an unhandled critical extension to be accepted. This only affects builds with CRL support enabled and where a crafted CRL had a trusted signature when parsed.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 06/26/2026
This vulnerability represents a critical flaw in certificate revocation list processing within cryptographic libraries that enables attackers to bypass important security controls through improper handling of critical extensions. The issue resides specifically in the ParseCRL_Extensions function where the system fails to properly enforce critical extension requirements, creating a pathway for malicious actors to craft specially formatted certificate revocation lists that contain unhandled critical extensions yet still be accepted as valid by the system.
The technical implementation flaw stems from inadequate validation mechanisms within the CRL parsing logic. When a certificate revocation list is processed, critical extensions are supposed to be strictly enforced according to established cryptographic standards and protocols. However, the ParseCRL_Extensions function does not properly validate that all critical extensions are either recognized and handled appropriately or that their presence would cause the entire CRL to be rejected as invalid. This creates a scenario where an attacker can inject a crafted CRL containing an unhandled critical extension that would normally trigger rejection but instead passes through undetected due to the missing enforcement mechanism.
The operational impact of this vulnerability is significant as it undermines the fundamental security guarantees provided by certificate revocation mechanisms. When systems accept CRLs with unhandled critical extensions, they may inadvertently process certificates that should have been rejected based on their revocation status or other security parameters. This affects all builds that have CRL support enabled and where a crafted CRL has a trusted signature when parsed, meaning that even legitimate certificate authorities could potentially be bypassed through this mechanism. The vulnerability essentially allows attackers to manipulate the certificate validation process without detection, potentially enabling unauthorized access or privilege escalation scenarios.
This weakness aligns with CWE-693 which describes protection mechanism failures where security mechanisms are not properly enforced, and represents a specific instance of improper enforcement of security policies within certificate validation systems. From an ATT&CK perspective, this vulnerability could be leveraged as part of a broader attack chain under techniques such as T1556 for credential access or T1071 for application layer protocol usage. The vulnerability is particularly concerning because it operates at the core of trust management systems where cryptographic validation occurs, potentially allowing attackers to establish persistent access or bypass security controls that are essential for maintaining secure communications and authentication processes.
The recommended mitigations include implementing strict enforcement of critical extension handling within the CRL parsing functions, ensuring that any unrecognized critical extensions immediately cause CRL rejection, and conducting thorough testing of certificate revocation list processing with various edge cases. Organizations should also consider implementing additional validation layers beyond basic signature verification to ensure that all components of certificate revocation lists are properly validated according to established cryptographic standards and that no unhandled critical extensions can slip through the validation process.