To report a security vulnerability/problem in AssaultCube (client, server, website), including exploits which lead to the crash of the clients or servers in multiplayer mode, please create an issue on GitHub titled: Security issue
For each reporter of the security issue a private project board will be created on GitHub, where he will be able to post the details for this and future security issues. A link to the private project board will be post in a comment for the issue.
Thanks!