CVE-2015-6112 in Windows
Summary
by MITRE
SChannel in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, and Windows RT Gold and 8.1 lacks the required extended master-secret binding support to ensure that a server's X.509 certificate is the same during renegotiation as it was before renegotiation, which allows man-in-the-middle attackers to obtain sensitive information or modify TLS session data via a "triple handshake attack," aka "Schannel TLS Triple Handshake Vulnerability."
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Analysis
by VulDB Data Team • 11/18/2024
The CVE-2015-6112 vulnerability represents a critical weakness in Microsoft Windows operating systems' Secure Channel (SChannel) implementation that specifically affects the TLS protocol handling during session renegotiation processes. This vulnerability stems from the absence of proper extended master-secret binding support, which is a fundamental security mechanism designed to maintain cryptographic consistency throughout TLS sessions. The flaw impacts a wide range of Microsoft operating systems including Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, and Windows RT Gold and 8.1, making it one of the most widespread TLS-related vulnerabilities in the Windows ecosystem. The vulnerability is particularly concerning because it enables attackers to perform man-in-the-middle attacks that can compromise the integrity and confidentiality of encrypted communications.
The technical flaw manifests when SChannel fails to properly validate that the server's X.509 certificate remains consistent during TLS session renegotiation processes. In standard TLS implementations, the extended master-secret extension ensures that the master secret derived during the initial handshake remains consistent throughout any subsequent renegotiations, preventing attackers from exploiting the session to substitute different certificates. However, Microsoft Windows SChannel implementation lacks this critical validation mechanism, creating a window of opportunity for attackers to perform what is known as a "triple handshake attack." This attack exploits the vulnerability by allowing an attacker to manipulate the TLS renegotiation process, potentially replacing the legitimate server certificate with a malicious one while maintaining the appearance of a legitimate connection.
The operational impact of CVE-2015-6112 is severe and multifaceted, affecting both the confidentiality and integrity of TLS-protected communications. Attackers can leverage this vulnerability to intercept, modify, or inject data into TLS sessions without detection, potentially compromising sensitive information such as login credentials, personal data, financial transactions, and business communications. The vulnerability specifically enables attackers to perform session hijacking attacks where they can modify session data while maintaining the illusion of a secure connection. This makes the attack particularly dangerous in enterprise environments where sensitive data flows through TLS-protected channels, as it can lead to data breaches, credential theft, and unauthorized access to corporate networks. The vulnerability affects both client and server implementations, meaning that systems can be compromised regardless of whether they are acting as clients or servers in TLS communications.
Mitigation strategies for CVE-2015-6112 focus on both immediate patching and operational security measures. Microsoft released security updates that addressed the vulnerability by implementing proper extended master-secret binding in SChannel, requiring administrators to apply the relevant security patches immediately. Organizations should also implement network monitoring solutions to detect anomalous TLS renegotiation patterns that might indicate exploitation attempts. Additional mitigations include disabling TLS renegotiation where possible, implementing strict certificate validation policies, and deploying intrusion detection systems that can identify triple handshake attack patterns. From a compliance perspective, this vulnerability aligns with CWE-327 (Use of a Broken or Risky Cryptographic Algorithm) and CWE-328 (Use of Weak Hash Algorithm) categories, and it maps to ATT&CK technique T1041 (Exfiltration Over C2 Channel) and T1566 (Phishing) as attackers may use the vulnerability to establish persistent access. Organizations should also consider implementing certificate pinning mechanisms and monitoring for unauthorized certificate changes during TLS sessions to provide additional layers of protection against this specific vulnerability.