YARA before v4.0.3 is vulnerable to buffer overflow in "dotnet" module. The strncpy function was being invoked with a source buffer that was shorter than MAX_TYPELIB_SIZE and the string was not null-terminated, which means that strncpy read past the end of the buffer. Now the limit pass to strncpy is the length of the string as indicated in the byte before the string itself. This length, being a byte, is equal to or less than MAX_TYPELIB_SIZE whose value is 255.