CVE-2025-15346 in wolfSSL-py
Summary
by MITRE • 01/08/2026
A vulnerability in the handling of verify_mode = CERT_REQUIRED in the wolfssl Python package (wolfssl-py) causes client certificate requirements to not be fully enforced.
Because the WOLFSSL_VERIFY_FAIL_IF_NO_PEER_CERT flag was not included, the behavior effectively matched CERT_OPTIONAL: a peer certificate was verified if presented, but connections were incorrectly authenticated when no client certificate was provided.
This results in improper authentication, allowing attackers to bypass mutual TLS (mTLS) client authentication by omitting a client certificate during the TLS handshake.
The issue affects versions up to and including 5.8.2.
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Analysis
by VulDB Data Team • 01/08/2026
The vulnerability identified as CVE-2025-15346 represents a critical flaw in the wolfssl Python package that undermines the security of mutual TLS implementations. This issue specifically targets the verification mode handling within the wolfssl-py library, where the CERT_REQUIRED setting fails to properly enforce client certificate requirements. The flaw stems from the absence of the WOLFSSL_VERIFY_FAIL_IF_NO_PEER_CERT flag during the TLS handshake process, which fundamentally alters the expected authentication behavior from what security practitioners would anticipate. When this flag is missing, the system effectively operates under CERT_OPTIONAL mode rather than the intended CERT_REQUIRED mode, creating a significant security gap that can be exploited by malicious actors.
The technical implementation of this vulnerability occurs at the TLS handshake level where wolfssl processes client certificate validation. In a properly configured CERT_REQUIRED environment, the TLS stack should mandate that a valid client certificate be presented and verified during the handshake process. However, due to the missing verification flag, the wolfssl library accepts connections even when no client certificate is provided, effectively allowing unauthenticated access to services that should require mutual TLS authentication. This misconfiguration creates a scenario where the security model of mutual TLS is completely bypassed, as the system fails to enforce the mandatory certificate verification step that should occur when CERT_REQUIRED is specified.
The operational impact of this vulnerability extends beyond simple authentication bypass to potentially compromise entire secure communication channels that rely on mutual TLS for protection. Attackers can exploit this weakness by simply omitting the client certificate during the TLS handshake process, thereby gaining access to services that should have required client authentication. This vulnerability directly violates the principle of least privilege and can lead to unauthorized access to sensitive data and resources. The flaw affects all versions up to and including 5.8.2, meaning that organizations using these versions are potentially exposing their systems to attacks that could compromise the confidentiality and integrity of their secure communications. This issue aligns with CWE-284, which addresses improper access control, and represents a clear violation of the security controls that should be enforced during TLS authentication.
Organizations utilizing the wolfssl Python package must immediately implement mitigations to address this vulnerability, including upgrading to patched versions of the library where the WOLFSSL_VERIFY_FAIL_IF_NO_PEER_CERT flag is properly implemented. System administrators should conduct comprehensive audits of their TLS configurations to ensure that mutual TLS requirements are correctly enforced and that no services are inadvertently operating under less secure CERT_OPTIONAL modes. Additionally, security monitoring should be enhanced to detect anomalous connection patterns that might indicate exploitation attempts. The ATT&CK framework categorizes this type of vulnerability under T1566, which deals with credential harvesting through network attacks, as attackers can leverage this flaw to bypass authentication mechanisms. Regular security assessments and penetration testing should be conducted to verify that the TLS implementations are functioning as intended and that all authentication requirements are properly enforced.