CVE-2015-8624 in MediaWiki
Summary
by MITRE
The User::matchEditToken function in includes/User.php in MediaWiki before 1.23.12, 1.24.x before 1.24.5, 1.25.x before 1.25.4, and 1.26.x before 1.26.1 does not perform token comparison in constant time before determining if a debugging message should be logged, which allows remote attackers to guess the edit token and bypass CSRF protection via a timing attack, a different vulnerability than CVE-2015-8623.
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Analysis
by VulDB Data Team • 09/12/2020
The vulnerability described in CVE-2015-8624 represents a critical security flaw in the MediaWiki content management system that affects multiple versions prior to specific patch releases. This issue resides within the User::matchEditToken function located in the includes/User.php file, which is a core component responsible for handling user authentication and authorization processes. The vulnerability specifically targets the token comparison mechanism used for CSRF (Cross-Site Request Forgery) protection, which is fundamental to preventing unauthorized modifications to wiki content. The flaw enables remote attackers to exploit timing variations in the token comparison process to systematically guess valid edit tokens and bypass essential security controls.
The technical implementation of this vulnerability stems from the function's failure to perform constant-time string comparison when validating edit tokens. In cryptographic operations, constant-time comparisons are essential to prevent timing attacks that rely on measuring the time difference between different comparison outcomes. When the system uses a standard string comparison that terminates early upon detecting a mismatch, attackers can measure the execution time of these comparisons to infer information about the correct token values. This timing information leak creates a side-channel attack vector that allows adversaries to iteratively guess the correct token through statistical analysis and timing measurements.
The operational impact of this vulnerability is significant as it directly undermines the CSRF protection mechanisms that are fundamental to web application security. An attacker who successfully exploits this vulnerability can bypass the token-based protection that prevents unauthorized users from making modifications to wiki content on behalf of authenticated users. This allows for unauthorized edits, potential data corruption, and in severe cases, complete compromise of the wiki's content integrity. The vulnerability is particularly dangerous in collaborative environments where multiple users contribute content, as it enables attackers to inject malicious content or modify existing information without proper authorization. The timing attack approach makes this vulnerability particularly insidious because it can be executed remotely without requiring any special privileges or access to the system itself.
The security implications extend beyond simple content modification to encompass broader system integrity concerns and potential escalation paths. This vulnerability aligns with CWE-347, which addresses improper certificate validation and weak cryptographic implementations, and relates to ATT&CK technique T1212, which covers exploitation of software vulnerabilities through timing attacks. Organizations running affected MediaWiki installations face substantial risk of content tampering, information disclosure, and potential data manipulation that could compromise the trustworthiness of their collaborative platforms. The vulnerability's presence in multiple version branches demonstrates the persistence of timing attack flaws in web application security implementations.
Mitigation strategies for this vulnerability require immediate patching of affected MediaWiki installations to versions that implement proper constant-time token comparison mechanisms. System administrators should prioritize updating to the patched versions 1.23.12, 1.24.5, 1.25.4, and 1.26.1 respectively, as these releases contain the necessary cryptographic fixes. Additionally, organizations should implement monitoring for suspicious editing patterns and consider additional security measures such as enhanced logging, rate limiting, and network-level protections. The fix typically involves implementing cryptographic libraries or custom functions that ensure all string comparisons take equal time regardless of input differences, thereby eliminating the timing side-channel that enabled the attack. Regular security audits and vulnerability assessments should be conducted to identify similar implementations of cryptographic functions that may be susceptible to timing attacks, ensuring comprehensive protection against similar vulnerabilities.