CVE-2015-2936 in MediaWiki
Summary
by MITRE
MediaWiki 1.24.x before 1.24.2, when using PBKDF2 for password hashing, allows remote attackers to cause a denial of service (CPU consumption) via a long password.
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Analysis
by VulDB Data Team • 05/03/2022
The vulnerability identified as CVE-2015-2936 represents a significant security flaw in MediaWiki versions 1.24.x prior to 1.24.2 that specifically affects systems utilizing PBKDF2 password hashing mechanisms. This vulnerability operates through a carefully crafted denial of service attack that exploits the computational overhead associated with PBKDF2 password verification processes. The flaw stems from the implementation's lack of proper input validation and resource management when processing excessively long passwords, creating an opportunity for malicious actors to consume disproportionate system resources.
The technical implementation of this vulnerability resides in the PBKDF2 password hashing algorithm's handling of input parameters. When MediaWiki processes a password through PBKDF2, it iterates through a specified number of rounds to strengthen the hash, but fails to impose reasonable limits on password length. Attackers can exploit this by submitting passwords of extreme length, causing the system to perform an excessive number of computational iterations that consume CPU resources at an alarming rate. This creates a scenario where legitimate users may experience service degradation or complete unavailability of the authentication system.
The operational impact of CVE-2015-2936 extends beyond simple service disruption to potentially compromise the overall system stability and availability. The vulnerability allows attackers to exhaust CPU cycles through relatively simple means, requiring minimal computational resources to execute effectively. This makes it particularly dangerous in environments where MediaWiki serves as a critical authentication platform for web applications, content management systems, or collaborative platforms. The attack can be executed remotely without requiring authentication, making it an attractive vector for malicious actors seeking to disrupt services.
From a cybersecurity perspective, this vulnerability aligns with CWE-400, which categorizes improper input validation as a fundamental weakness in software design. The flaw demonstrates a classic example of resource exhaustion through malformed input, where the system fails to implement proper bounds checking or rate limiting mechanisms. The vulnerability also maps to ATT&CK technique T1499.004, which covers network denial of service attacks, specifically highlighting the exploitation of system resources through computational overhead. Organizations implementing MediaWiki should prioritize immediate patching to address this vulnerability, as it represents a straightforward attack vector that can be executed with minimal technical expertise.
The remediation strategy for CVE-2015-2936 involves upgrading to MediaWiki version 1.24.2 or later, which includes proper input validation and resource management for PBKDF2 password hashing. Additionally, system administrators should implement rate limiting mechanisms and input length restrictions to prevent similar vulnerabilities from manifesting in other components of their infrastructure. The fix addresses the root cause by enforcing reasonable password length limits and ensuring that PBKDF2 iterations do not consume excessive computational resources, thereby maintaining system responsiveness and availability for legitimate users.