CVE-2014-0139 in cURL
Summary
by MITRE
cURL and libcurl 7.1 before 7.36.0, when using the OpenSSL, axtls, qsossl or gskit libraries for TLS, recognize a wildcard IP address in the subject's Common Name (CN) field of an X.509 certificate, which might allow man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority.
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Analysis
by VulDB Data Team • 05/10/2026
The vulnerability identified as CVE-2014-0139 represents a critical security flaw in cURL and libcurl versions prior to 7.36.0 that affects TLS implementations using OpenSSL, axtls, qsossl, or gskit libraries. This issue stems from the improper handling of wildcard IP addresses within the Common Name field of X.509 certificates, creating a significant bypass of SSL/TLS certificate validation mechanisms. The flaw allows malicious actors to exploit the certificate validation process by crafting certificates that appear legitimate while actually enabling unauthorized man-in-the-middle attacks against SSL servers.
The technical root cause of this vulnerability lies in the certificate validation logic within cURL's TLS implementation where wildcard IP addresses in the subject's Common Name field are accepted without proper validation. When a certificate contains a wildcard IP address in the CN field, the system incorrectly treats it as a valid match for any IP address, effectively bypassing the normal certificate verification process that should ensure the certificate's authenticity and intended server identity. This behavior violates the fundamental principles of certificate-based authentication that rely on strict matching between the certificate's subject and the target server's identity. The vulnerability specifically affects the certificate validation routine where the system should enforce strict hostname matching but instead accepts wildcard IP patterns, creating a security gap that can be exploited by attackers.
The operational impact of this vulnerability is severe and far-reaching across organizations relying on cURL or libcurl for secure communications. An attacker with access to a legitimate Certification Authority's certificate could create a malicious certificate containing a wildcard IP address in the CN field, enabling them to impersonate any server within the wildcard domain. This creates a significant risk for web services, API communications, and any application that uses cURL for secure network connections. The vulnerability particularly affects systems where SSL/TLS is used for authentication and encryption, as it undermines the entire certificate trust model. Organizations using vulnerable versions of cURL may experience unauthorized access to sensitive data, session hijacking, and complete compromise of secure communication channels.
The security implications of CVE-2014-0139 align with CWE-295, which addresses improper certificate validation, and maps to ATT&CK technique T1046 for network service scanning and T1566 for credential access through man-in-the-middle attacks. This vulnerability demonstrates the critical importance of proper certificate validation implementation and highlights the risks associated with legacy TLS implementations that fail to properly enforce certificate constraints. Organizations should immediately update to cURL version 7.36.0 or later to address this vulnerability, as the patch resolves the improper handling of wildcard IP addresses in certificate Common Name fields. Additionally, security teams should conduct comprehensive vulnerability assessments to identify any systems still running vulnerable versions of cURL and implement network monitoring to detect potential exploitation attempts. The fix ensures that wildcard IP addresses are properly validated against the actual server IP addresses, restoring the intended security controls for SSL/TLS certificate verification.