Mongoose is an embedded web server and network library. Prior to 7.22, an attacker who can control an SSI-enabled file can place directory traversal sequences in an #include file or #include virtual directive. The mg ssi() function in src/ssi.c concatenates the directive argument into a filesystem path without calling mg path is sane(), allowing an MG ENABLE SSI deployment with ssi pattern configured to disclose files readable by the Mongoose process. This issue is fixed in version 7.22.