CVE-2014-2900 in CyaSSL
Summary
by MITRE
wolfSSL CyaSSL before 2.9.4 does not properly validate X.509 certificates with unknown critical extensions, which allows man-in-the-middle attackers to spoof servers via crafted X.509 certificate.
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Analysis
by VulDB Data Team • 05/11/2026
The vulnerability identified as CVE-2014-2900 affects wolfSSL CyaSSL implementations prior to version 2.9.4, representing a critical security flaw in X.509 certificate validation mechanisms. This weakness stems from the software's improper handling of certificates containing unknown critical extensions, creating a significant attack surface that adversaries can exploit to conduct man-in-the-middle operations. The flaw specifically targets the certificate validation process where the system fails to adequately verify the presence of critical extensions that should trigger immediate validation failure or require explicit handling by the certificate processing framework.
The technical root cause of this vulnerability lies in the certificate validation logic that does not enforce strict validation rules for critical extensions within X.509 certificates. According to CWE-310, this represents a weakness in cryptographic key handling where the system fails to properly validate certificate attributes that are designated as critical. The implementation follows a permissive validation approach that accepts certificates containing unknown critical extensions rather than rejecting them outright, which violates fundamental security principles for certificate validation. This behavior creates a scenario where an attacker can craft a malicious certificate with unknown critical extensions that will be accepted by vulnerable systems, effectively bypassing the certificate validation process.
The operational impact of this vulnerability is severe and directly enables man-in-the-middle attacks against systems using affected wolfSSL implementations. Attackers can generate and present X.509 certificates that contain unknown critical extensions, which the vulnerable software will accept without proper validation, allowing them to impersonate legitimate servers and intercept or modify communications. This vulnerability affects any system relying on wolfSSL for secure communications, including web servers, email servers, and other applications that depend on SSL/TLS certificate validation for authentication and encryption. The attack vector is particularly dangerous because it operates silently, allowing the attacker to establish trust relationships with clients without detection, as the certificate validation process fails to identify the malicious certificate as invalid.
This vulnerability aligns with several ATT&CK techniques including T1552.001 for credentials in files and T1046 for network service scanning, as attackers can leverage the compromised certificate validation to establish unauthorized communication channels. The flaw also relates to T1592.002 for threat actor reconnaissance, as adversaries can identify vulnerable systems through certificate validation testing. Organizations using affected wolfSSL versions face significant risk of data interception, authentication bypass, and potential system compromise. The vulnerability demonstrates poor adherence to security best practices outlined in NIST SP 800-57 for cryptographic key management and certificate validation, where critical extensions must be properly handled or rejected to maintain security integrity.
The recommended mitigation strategy involves upgrading to wolfSSL CyaSSL version 2.9.4 or later, which implements proper validation of critical extensions in X.509 certificates. Administrators should also implement certificate pinning mechanisms where possible, deploy additional monitoring for certificate validation failures, and ensure that all systems using SSL/TLS are regularly updated with the latest security patches. Security teams should conduct comprehensive vulnerability assessments to identify all systems using affected versions of wolfSSL and implement network segmentation to limit the potential impact of successful attacks. The fix addresses the core validation issue by ensuring that certificates containing unknown critical extensions are rejected during the validation process, thereby preventing the man-in-the-middle scenarios that this vulnerability enables.