MyBB Server-Side Request Forgery Vulnerability in Theme Import Function

A server-side request forgery (SSRF) vulnerability has been identified in MyBB version 1.8.38. This issue arises in the 'Import a Theme' function, which allows remote attackers to make web requests to arbitrary locations. Exploitation of this vulnerability could enable attackers to query and modify information from internal services.

Impact

Exploitation of this vulnerability could lead to unauthorized access to internal services, allowing attackers to query and potentially modify sensitive information.

Reproduction

To reproduce this vulnerability, use the 'Import a Theme' function in MyBB 1.8.38. When prompted to enter a URL, provide a link that points to a resource capable of receiving and responding to HTTP requests. The application will fetch the URL, thereby exploiting the SSRF vulnerability by allowing requests to internal services or private hosts, as configured in the MyBB 'disallowed_remote_hosts' and 'disallowed_remote_addresses' settings.

Remediation

MyBB administrators can limit access to private hosts and IP addresses by updating the 'disallowed_remote_hosts' and 'disallowed_remote_addresses' arrays in the MyBB configuration file. This will help mitigate the SSRF vulnerability by preventing the application from making requests to specified hosts or addresses.