CURL-CVE-2020-8285

FTP wildcard stack overflow

libcurl offers a wildcard matching functionality, which allows a callback (set with `CURLOPT_CHUNK_BGN_FUNCTION`) to return information back to libcurl on how to handle a specific entry in a directory when libcurl iterates over a list of all available entries. When this callback returns `CURL_CHUNK_BGN_FUNC_SKIP`, to tell libcurl to not deal with that file, the internal function in libcurl then calls itself recursively to handle the next directory entry. If there is a sufficient amount of file entries and if the callback returns "skip" enough number of times, libcurl runs out of stack space. The exact amount does of course vary with platforms, compilers and other environmental factors. The content of the remote directory is not kept on the stack, so it seems hard for the attacker to control exactly what data that overwrites the stack - however it remains a Denial-Of-Service vector as a malicious user who controls a server that a libcurl-using application works with under these premises can trigger a crash. (There is also a few other ways the function can be made to call itself and trigger this problem.)