CVE-2015-8623 in MediaWiki
Summary
by MITRE
The User::matchEditToken function in includes/User.php in MediaWiki before 1.23.12 and 1.24.x before 1.24.5 does not perform token comparison in constant time before returning, which allows remote attackers to guess the edit token and bypass CSRF protection via a timing attack, a different vulnerability than CVE-2015-8624.
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Analysis
by VulDB Data Team • 09/12/2020
The vulnerability described in CVE-2015-8623 represents a critical security flaw in the MediaWiki content management system that affects versions prior to 1.23.12 and 1.24.x before 1.24.5. This issue resides within the User::matchEditToken function located in the includes/User.php file, which is responsible for validating edit tokens used to prevent cross-site request forgery attacks. The flaw enables remote attackers to exploit timing variations in token comparison operations to guess valid edit tokens and subsequently bypass the CSRF protection mechanisms that are fundamental to preventing unauthorized modifications to wiki content. The vulnerability specifically relates to the lack of constant-time token comparison, which creates measurable timing differences that can be exploited through statistical analysis and repeated attempts.
The technical implementation of this vulnerability stems from the function's failure to use constant-time comparison algorithms when validating edit tokens. In cryptographic operations, constant-time comparison is essential to prevent timing attacks where an attacker can measure the time taken to compare two values and infer information about the correct value based on timing variations. When a function performs a simple string comparison with early termination upon finding a mismatch, the time taken to complete the comparison varies depending on the position of the first differing character. This timing differential provides attackers with information that can be systematically exploited to reconstruct valid tokens through repeated testing. The vulnerability operates under the Common Weakness Enumeration category CWE-203, which specifically addresses "Information Disclousure via Timing Variations" and falls under the broader category of CWE-347, "Improper Verification of Cryptographic Signature."
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables attackers to perform unauthorized modifications to wiki content through crafted requests that leverage the guessed edit tokens. This represents a significant threat to wiki integrity and content security, as attackers can modify pages, inject malicious content, or manipulate wiki data without proper authentication. The vulnerability also affects the broader MediaWiki ecosystem where wiki administrators rely on CSRF protection to maintain content integrity and prevent unauthorized edits. The timing attack approach allows attackers to systematically work through potential token values, making this exploitation method particularly dangerous as it can be automated and does not require any special privileges or access to the system's internal workings. According to ATT&CK framework, this vulnerability maps to T1078.004 "Valid Accounts: SSH Keys" and T1566.001 "Phishing: Spearphishing Attachment" as attackers can leverage this weakness to bypass security controls and perform unauthorized modifications to wiki content.
Mitigation strategies for CVE-2015-8623 primarily focus on upgrading to patched versions of MediaWiki where the User::matchEditToken function has been modified to use constant-time comparison algorithms. The recommended remediation involves immediate deployment of MediaWiki versions 1.23.12 or 1.24.5 and later, which implement proper constant-time token comparison. Organizations should also consider implementing additional monitoring and logging of edit token usage to detect potential exploitation attempts. Security teams should review their MediaWiki configurations and ensure that CSRF protection mechanisms are properly enforced throughout the application. The fix typically involves replacing standard string comparison operations with cryptographic comparison functions that take constant time regardless of input values. Additionally, administrators should consider implementing rate limiting and additional authentication controls for sensitive operations to provide defense-in-depth against potential exploitation attempts.