stb_vorbis is a single file MIT licensed library for processing ogg vorbis files. A crafted file may trigger out of bounds write in "f->vendor[len] = (char)'\0';". The root cause is that if the len read in "start_decoder" is "-1" and "len + 1" becomes 0 when passed to "setup_malloc". The "setup_malloc" behaves differently when "f->alloc.alloc_buffer" is pre-allocated. Instead of returning "NULL" as in "malloc" case it shifts the pre-allocated buffer by zero and returns the currently available memory block. This issue may lead to code execution.