CVE-2010-4626 in MyBB
Summary
by MITRE
The my_rand function in functions.php in MyBB (aka MyBulletinBoard) before 1.4.12 does not properly use the PHP mt_rand function, which makes it easier for remote attackers to obtain access to an arbitrary account by requesting a reset of the account s password, and then conducting a brute-force attack.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 10/07/2021
The vulnerability described in CVE-2010-4626 resides in the my_rand function implementation within the functions.php file of MyBB versions prior to 1.4.12. This flaw represents a critical weakness in the software's cryptographic randomness generation, directly impacting the security of password reset functionality. The issue stems from improper utilization of PHP's mt_rand function, which is a multiply-with-carry pseudo-random number generator designed for high-quality random number generation. When MyBB's custom my_rand function fails to properly initialize or seed the underlying mt_rand function, it creates predictability in the random number sequences used for security purposes.
The operational impact of this vulnerability extends beyond simple randomness issues to compromise the entire account recovery mechanism. Attackers can exploit this weakness by initiating password reset requests for target accounts and then conducting systematic brute-force attacks against the predictable reset tokens or temporary passwords generated by the flawed random number generator. This vulnerability directly violates security principle of entropy in cryptographic systems, as defined by CWE-330, which addresses the use of insufficiently random values in security contexts. The predictability introduced by the flawed implementation means that attackers can significantly reduce the search space required for successful password recovery exploitation, making account takeovers more feasible.
The technical flaw manifests specifically in how the random number generation process is initialized within MyBB's custom function, likely failing to properly seed the mt_rand function with sufficient entropy from system sources such as /dev/urandom or other hardware-based random number generators. This improper seeding creates deterministic sequences that can be reconstructed by attackers who observe or guess the initial state of the random number generator. The vulnerability aligns with ATT&CK technique T1566.002, which involves credential access through social engineering and password reset manipulation, and specifically targets the credential exposure phase of attack chains. Security practitioners should note that this issue represents a fundamental flaw in the application's security architecture rather than a simple configuration error.
Mitigation strategies for this vulnerability require immediate patching of MyBB installations to version 1.4.12 or later, where the random number generation has been properly implemented. Organizations should also implement additional security controls such as rate limiting on password reset requests, account lockout mechanisms after failed reset attempts, and monitoring for unusual patterns in password reset activity. The fix typically involves ensuring that the mt_rand function receives proper seeding from secure entropy sources, and that the random number generation process is properly initialized before any security-sensitive operations are performed. This vulnerability underscores the critical importance of proper random number generation in cryptographic systems and demonstrates how seemingly minor implementation flaws can create significant security risks, particularly in authentication and account recovery mechanisms that are fundamental to web application security.