CVE-2025-46171 is a denial-of-service (DoS) vulnerability affecting vBulletin version 3.8.7, a widely used forum software platform. The vulnerability arises from the misc.php?do=buddylist endpoint, which processes a user's buddy list. When an authenticated user has a very large buddy list, the processing of this list consumes excessive memory resources. This memory exhaustion can overwhelm the server hosting the forum, leading to a crash or severe degradation of service availability. The vulnerability requires authentication, meaning an attacker must have a valid user account on the forum to exploit it. However, no user interaction beyond the attacker’s own actions is needed. The flaw is rooted in inefficient handling of large buddy lists, which causes the server to allocate more memory than it can sustain, resulting in resource exhaustion. There are no known exploits in the wild at this time, and no patches or fixes have been publicly released. The absence of a CVSS score indicates that the vulnerability has not yet been fully assessed for severity by standard scoring systems. The vulnerability primarily impacts the availability of the forum service, with no direct indication of confidentiality or integrity compromise. Since the vulnerability is triggered by authenticated users with large buddy lists, the scope is limited to forums running this specific vBulletin version and having users with extensive buddy lists.

For European organizations using vBulletin 3.8.7 to host community forums, customer support portals, or internal collaboration platforms, this vulnerability poses a risk of service disruption. An attacker with a valid account could intentionally create or maintain a large buddy list to trigger the DoS condition, causing the forum server to crash or become unresponsive. This could lead to downtime, loss of user trust, and potential operational disruption, especially if the forum is critical for customer engagement or internal communications. Although the vulnerability does not directly expose sensitive data or allow privilege escalation, the resulting unavailability could indirectly impact business continuity and reputation. Organizations in sectors such as e-commerce, education, and public services that rely on vBulletin forums for user interaction may experience significant inconvenience or loss of service. Furthermore, the requirement for authentication limits the attack surface but does not eliminate risk, as attackers could create accounts or compromise existing ones. The lack of a patch means organizations must rely on mitigation strategies until an official fix is available.

European organizations should implement several targeted mitigation strategies to reduce risk from CVE-2025-46171. First, restrict the maximum size of buddy lists at the application or database level to prevent excessively large lists from being created or maintained. This can be enforced through input validation or custom code modifications. Second, monitor user buddy list sizes and set alerts for unusually large lists that could indicate abuse. Third, implement rate limiting and session management controls to detect and block suspicious activity from authenticated users attempting to exploit this vulnerability. Fourth, consider isolating the forum server or running it with resource limits (e.g., memory quotas, containerization) to prevent a single process from exhausting system resources. Fifth, evaluate upgrading to a newer, supported version of vBulletin or alternative forum software that does not have this vulnerability. Finally, maintain robust account management policies, including strong authentication and monitoring for compromised accounts, to reduce the risk of attacker access. Since no official patch is currently available, these practical controls are critical to mitigating impact.