Exposure of Sensitive Information to an Unauthorized Actor
The Admin control panel in MyBB (aka MyBulletinBoard) before 1.8.7 and MyBB Merge System before 1.8.7 allows remote attackers to obtain the installation path via vectors involving sending mails.
CWE-200 - Information Exposure
An information exposure vulnerability is categorized as an information flow (IF) weakness, which can potentially allow unauthorized access to otherwise classified information in the application, such as confidential personal information (demographics, financials, health records, etc.), business secrets, and the application's internal environment.