CVE-2014-8151 in libcURL
Summary
by MITRE
The darwinssl_connect_step1 function in lib/vtls/curl_darwinssl.c in libcurl 7.31.0 through 7.39.0, when using the DarwinSSL (aka SecureTransport) back-end for TLS, does not check if a cached TLS session validated the certificate when reusing the session, which allows man-in-the-middle attackers to spoof servers via a crafted certificate.
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Analysis
by VulDB Data Team • 02/02/2025
The vulnerability identified as CVE-2014-8151 resides within the libcurl library's implementation of the DarwinSSL (SecureTransport) back-end for TLS communication. This flaw affects versions 7.31.0 through 7.39.0 and specifically targets the darwinssl_connect_step1 function which handles the initial TLS connection establishment process. The core issue manifests when the library attempts to reuse cached TLS sessions, failing to validate whether the original session's certificate validation was properly completed before proceeding with the reuse operation. This oversight creates a critical security gap that undermines the fundamental purpose of certificate validation in TLS protocols.
The technical flaw stems from the improper handling of TLS session resumption mechanisms within the DarwinSSL implementation. When a client establishes a TLS connection and subsequently attempts to resume a previous session, the system should verify that the certificate validation process was completed successfully during the initial handshake. However, the vulnerable implementation bypasses this crucial verification step, allowing cached sessions to be reused even when the original certificate validation may have been compromised. This behavior aligns with CWE-295 which addresses improper certificate validation and represents a significant deviation from proper TLS security practices. The vulnerability essentially allows an attacker to exploit the session caching mechanism to bypass certificate validation entirely.
The operational impact of this vulnerability is severe and directly enables man-in-the-middle attacks against systems using affected versions of libcurl. Attackers can craft specially designed certificates that would be accepted by the system even though they should be rejected based on proper certificate validation. This creates a scenario where legitimate users may unknowingly establish secure connections with malicious servers that present forged certificates. The vulnerability affects any application or system that relies on libcurl's SecureTransport back-end for TLS communication, including web browsers, email clients, and various network utilities. The attack vector is particularly concerning because it operates silently, without alerting users to the compromised connection, and can persist across multiple sessions due to the caching mechanism.
Mitigation strategies for CVE-2014-8151 primarily involve upgrading to libcurl versions 7.39.1 or later where the vulnerability has been addressed through proper session validation checks. Organizations should implement comprehensive patch management procedures to ensure all affected systems are updated promptly. Additionally, security teams should consider implementing network monitoring to detect anomalous TLS behavior that might indicate exploitation attempts. The fix implemented by the libcurl development team typically involves adding explicit validation checks for cached sessions to ensure that certificate validation was properly completed before allowing session reuse. This approach aligns with ATT&CK technique T1573.002 which covers secure transport layer protocols and emphasizes the importance of proper session management and validation in maintaining secure communications. Organizations should also consider implementing additional security controls such as certificate pinning for critical applications to provide defense-in-depth against similar vulnerabilities.