GHSA-cjmx-764f-286c: Mongoose: Heap OOB reads and null-byte bypass in mg_path_is_sane (util.c)

Mongoose is an embedded web server and network library. Prior to 7.22, mgpathissane in src/util.c read path.buf[1] without first requiring path.len to be at least two and read s[2] when only two bytes remained. Unauthenticated remote requests reaching mghttpupload or mghttpservedir with the affected short path shapes could therefore trigger one-byte heap out-of-bounds reads. On bare-metal or RTOS targets without memory protection, the adjacent byte could be exposed or influence whether a path was accepted, and instrumented builds could crash. This issue is fixed in version 7.22.