Source: cve@mitre.org
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.
MyBB versions prior to 1.4.12 are vulnerable to a critical account takeover vulnerability. The flawed implementation of the my_rand function in functions.php allows attackers to predict the random numbers used for password reset tokens, enabling them to brute-force their way into user accounts. Successful exploitation grants unauthorized access, potentially leading to data breaches and system compromise.
Step 1: Account Reset Request: The attacker initiates a password reset request for a target account. This triggers MyBB to generate a unique token and send a password reset link to the associated email address.
Step 2: Token Prediction: The attacker leverages the knowledge of the flawed my_rand implementation to predict the possible values of the reset token. This is possible due to the lack of proper seeding of the random number generator.
Step 3: Brute-Force Attack: The attacker uses the predicted token values to attempt password resets. They submit the predicted tokens along with the target username.
Step 4: Successful Reset: If the attacker's predicted token matches the one generated by the server, the password reset is successful, and the attacker gains control of the account.
The vulnerability stems from the improper use of the PHP mt_rand function within the my_rand function in MyBB's functions.php file. The my_rand function was intended to generate cryptographically secure random numbers for password reset tokens. However, the implementation failed to properly seed the mt_rand function, leading to predictable output. This predictability allows an attacker to generate a limited set of possible tokens, significantly reducing the search space for a brute-force attack. The lack of proper seeding effectively makes the random number generation deterministic, allowing an attacker to calculate the same tokens generated by the server. This is not a buffer overflow or SQL injection vulnerability, but a weakness in the random number generation, making password reset tokens easily guessable.
While no specific APT groups are directly linked to this CVE, the nature of the vulnerability makes it attractive to a wide range of attackers, including those seeking initial access or account takeover. This vulnerability could be leveraged by attackers to gain a foothold in a system and then deploy malware or conduct further attacks. CISA KEV status: Not listed.
Monitor web server logs for suspicious password reset attempts, especially those originating from a single IP address or a small range of IP addresses.
Analyze network traffic for unusual patterns related to password reset requests, such as a high frequency of requests or requests with unusual parameters.
Implement intrusion detection systems (IDS) with rules to detect brute-force attempts against password reset functionality.
Review web server access logs for requests to member.php?action=lostpw or similar password reset endpoints, looking for repeated attempts with different parameters.
Upgrade MyBB to version 1.4.12 or later. This is the primary and most effective remediation step.
If upgrading is not immediately possible, implement a strong password policy requiring complex passwords.
Implement rate limiting on password reset attempts to mitigate brute-force attacks.
Consider implementing two-factor authentication (2FA) for all user accounts.
Regularly audit and review server logs for suspicious activity.
Ensure that the web server is properly configured and hardened to prevent other vulnerabilities that could be exploited in conjunction with this one.