Source: cve@mitre.org
MyBB (aka MyBulletinBoard) before 1.4.12 does not properly restrict uid values for group join requests, which allows remote attackers to cause a denial of service (resource consumption) by using guest access to submit join request forms for moderated groups, related to usercp.php and managegroup.php.
MyBB versions prior to 1.4.12 are vulnerable to a denial-of-service (DoS) attack. By exploiting a flaw in how group join requests are handled, attackers can exhaust server resources, rendering the forum unavailable to legitimate users. This vulnerability allows attackers to leverage guest access to submit a large number of malicious requests.
Step 1: Guest Access: The attacker, without needing an account, accesses the MyBB forum as a guest.
Step 2: Request Construction: The attacker crafts a malicious request to join a moderated group. This request is typically submitted through the user control panel (usercp.php) or group management interface (managegroup.php).
Step 3: UID Manipulation: The attacker manipulates the uid parameter within the join request. This parameter is intended to specify the user attempting to join the group, but the vulnerability allows the attacker to specify arbitrary or numerous uid values.
Step 4: Request Submission: The attacker submits the crafted join request, potentially repeatedly, to the vulnerable MyBB installation.
Step 5: Resource Exhaustion: The MyBB server processes the malicious requests. Due to the lack of proper validation, the server attempts to process each request, leading to excessive database queries, memory allocation, and CPU usage.
Step 6: Denial of Service: The server's resources are exhausted, causing a denial-of-service. Legitimate users are unable to access the forum due to the server's inability to handle their requests.
The vulnerability stems from a lack of proper input validation and authorization checks when processing group join requests, specifically related to the uid parameter. The MyBB software fails to adequately restrict the uid values used in requests to join moderated groups. An attacker can manipulate this uid parameter to submit a large number of join requests, effectively flooding the server with processing tasks. This leads to excessive resource consumption, including database queries and memory allocation, ultimately causing a denial-of-service. The core issue lies in the absence of checks to ensure the uid corresponds to a valid user or that the request originates from an authorized user. The usercp.php and managegroup.php files are directly involved in processing these requests, making them the attack surface.
While no specific APTs are directly linked to this vulnerability, it's a type of attack that could be used by any attacker to disrupt service. The ease of exploitation makes it a potential target for script kiddies and opportunistic attackers. Not listed on CISA KEV.
Monitor server logs for a sudden spike in requests to usercp.php or managegroup.php, especially from guest users.
Analyze web server access logs for unusual patterns of requests, such as a large number of requests with manipulated uid parameters.
Monitor database server performance for increased query load and resource consumption.
Implement intrusion detection systems (IDS) with rules to detect malicious requests targeting the vulnerable endpoints.
Use a web application firewall (WAF) to filter out suspicious traffic and block requests with invalid uid values.
Upgrade to MyBB version 1.4.12 or later.
Implement input validation to ensure the uid parameter is a valid user ID and that the user is authorized to join the group.
Implement rate limiting to restrict the number of group join requests from a single IP address or user within a specific timeframe.
Review and harden the web server configuration to prevent resource exhaustion.
Regularly scan the system for vulnerabilities and apply security patches promptly.
Implement a web application firewall (WAF) to filter malicious traffic.