CVE-2015-5267 in Moodle
Summary
by MITRE
lib/moodlelib.php in Moodle through 2.6.11, 2.7.x before 2.7.10, 2.8.x before 2.8.8, and 2.9.x before 2.9.2 relies on the PHP mt_rand function to implement the random_string and complex_random_string functions, which makes it easier for remote attackers to predict password-recovery tokens via a brute-force approach.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2015-5267 affects the Moodle learning management system across multiple version branches including 2.6.11 and earlier, 2.7.x versions before 2.7.10, 2.8.x versions before 2.8.8, and 2.9.x versions before 2.9.2. This security flaw resides within the lib/moodlelib.php file and specifically impacts the random_string and complex_random_string functions that are critical for generating password recovery tokens and other security-related identifiers. The issue stems from the reliance on PHP's built-in mt_rand function which is not cryptographically secure, creating predictable patterns that adversaries can exploit through brute-force attacks.
The technical implementation flaw occurs because the mt_rand function in php generates pseudo-random numbers using a linear congruential generator algorithm that has known weaknesses in cryptographic contexts. When Moodle uses this function to create password recovery tokens, the resulting sequences exhibit statistical patterns that make them vulnerable to prediction attacks. Attackers can potentially reverse-engineer the seed value used by mt_rand based on observed token patterns, thereby compromising the security of password reset functionality and user account recovery processes. This weakness directly violates the principle of cryptographic randomness required for security tokens and demonstrates a failure to implement proper cryptographically secure random number generation.
The operational impact of this vulnerability extends beyond simple password recovery token prediction to potentially enable broader account compromise scenarios. Remote attackers who successfully predict recovery tokens can gain unauthorized access to user accounts, potentially leading to data breaches, privilege escalation, and unauthorized modifications to course content or user information. The vulnerability affects the core authentication and authorization mechanisms within Moodle, making it particularly dangerous as it undermines fundamental security controls. Organizations using affected Moodle versions face increased risk of credential compromise and unauthorized access to educational platforms containing sensitive student and institutional data.
Security mitigations for CVE-2015-5267 require immediate patching to the affected Moodle versions, with administrators upgrading to the patched releases that address the random number generation issue. The recommended solution involves replacing the mt_rand function calls with cryptographically secure alternatives such as PHP's random_int or random_bytes functions, or implementing proper seeding mechanisms that ensure sufficient entropy for security tokens. Organizations should also conduct thorough security assessments of their Moodle installations, reviewing all functions that generate security tokens and ensuring that proper cryptographic practices are implemented. This vulnerability aligns with CWE-330, which describes insufficient entropy in random number generators, and represents a clear violation of ATT&CK technique T1566 related to credential access through social engineering and brute force attacks. Additionally, the issue demonstrates the importance of following secure coding practices as outlined in OWASP Top 10 and NIST guidelines for cryptographic implementation, particularly in the context of authentication and session management functions.