The Unreal engine is affected by some format string vulnerabilities which can be exploited by a malicious server when the victim client connects to it. The main format string can be exploited through a malformed CLASS parameter of the DLMGR command but another one seems to be exploitable through the forcing of the download of a malformed package (PKG). Some older games instead can be exploited through a malformed LEVEL parameter of the WELCOME command. The bug is caused by the calling of _vsnwprintf_s or _vsnwprintf for building an error message to visualize to the user (for example for a missing class) using a max size of 4 kilobytes and, naturally, without passing the needed format argument. All related exploit code is included in this tarball.