member.php in MyBB (aka MyBulletinBoard) before 1.4.12 makes a certain superfluous call to the SQL COUNT function, which allows remote attackers to cause a denial of service (resource consumption) by making requests to member.php that trigger scans of the entire users table.
CVE-2010-4628 is a denial-of-service (DoS) vulnerability in MyBB forum software that allows attackers to exhaust server resources. By sending crafted requests to member.php, attackers can trigger a superfluous SQL COUNT query against the entire users table, leading to significant performance degradation and potential service unavailability.
Step 1: Request Initiation: The attacker sends multiple HTTP requests to member.php on the vulnerable MyBB forum. These requests can be crafted to appear legitimate or can be randomized to avoid detection.
Step 2: Triggering the Vulnerability: Each request to member.php triggers the vulnerable code, which includes the superfluous COUNT query against the users table.
Step 3: Database Overload: The database server processes each COUNT query, scanning the entire users table for each request. This process consumes significant resources.
Step 4: Resource Exhaustion: As the number of requests increases, the database server becomes overloaded, leading to high CPU usage, memory consumption, and I/O bottlenecks.
Step 5: Denial of Service: The overloaded database server is unable to respond to legitimate requests from users, resulting in slow performance or complete service unavailability.
The vulnerability stems from an inefficient SQL query within member.php in MyBB versions prior to 1.4.12. Specifically, the code makes an unnecessary call to the COUNT function against the users table. This query is executed for each request to member.php, regardless of its actual purpose. When an attacker sends a large number of requests, this results in a massive number of COUNT queries, overwhelming the database server and consuming excessive resources like CPU, memory, and I/O. The root cause is a lack of optimization in the code, leading to an inefficient query that is executed unnecessarily. This is not a classic buffer overflow or race condition, but a resource exhaustion vulnerability.