A command inject vulnerability allows an attacker to perform command injection on Windows applications that indirectly depend on the CreateProcess function when the specific conditions are satisfied.

Summary The patch that addressed CVE-2023-40581 attempted to prevent RCE when using --exec with %q by replacing double quotes with two double quotes. However, this escaping is not sufficient, and still allows expansion of environment variables.

Support for output template expansion in --exec, along with this vulnerable behavior, was added to yt-dlp in version 2021.04.11.

cmd yt-dlp "https://youtu.be/42xO6rVqf2E" --ignore-config -f 18 --exec "echo %(title)q" [youtube] Extracting URL: https://youtu.be/42xO6rVqf2E [youtube] 42xO6rVqf2E: Downloading webpage [youtube] 42xO6rVqf2E: Downloading ios player API JSON [youtube] 42xO6rVqf2E: Downloading android player API JSON [youtube] 42xO6rVqf2E: Downloading m3u8 information [info] 42xO6rVqf2E: Downloading 1 format(s): 18 [download] Destination: %CMDCMDLINE：~-1%&echo pwned&calc.exe [42xO6rVqf2E].mp4 [download] 100% of 126.16KiB in 00:00:00 at 2.46MiB/s [Exec] Executing command: echo "%CMDCMDLINE:~-1%&echo pwned&calc.exe" "" pwned

Patches yt-dlp version 2024.04.09 fixes this issue by properly escaping %. It replaces them with %%cd:~,%, a variable that expands to nothing, leaving only the leading percent.

Workarounds It is recommended to upgrade yt-dlp to version 2024.04.09 as soon as possible. Also, always be careful when using --exec, because while this specific vulnerability has been patched, using unvalidated input in shell commands is inherently dangerous.

For Windows users who are not able to upgrade: - Avoid using any output template expansion in --exec other than {} (filepath). - If expansion in --exec is needed, verify the fields you are using do not contain %, ", | or &. - Instead of using --exec, write the info json and load the fields from it instead.

Details When escaping variables, the following code is used for Windows. ytdlp/compat/init.py line 31-33 python def compatshlexquote(s): import re return s if re.match(r'^[-\w./]+$', s) else s.replace('"', '""').join('""') It replaces " with "" to balance out the quotes and keep quoting intact if non-allowed characters are included. However, the %CMDCMDLINE% variable can be used to generate a quote using %CMDCMDLINE:~-1%; since the value of %CMDCMDLINE% is the commandline with which cmd.exe was called, and it is always called with the command surrounded by quotes, %CMDCMDLINE:~-1% expands to ". After the quotes have been unbalanced, special characters are no longer quoted and commands can be executed: cmd %CMDCMDLINE:~-1%&calc.exe

References - https://github.com/yt-dlp/yt-dlp/security/advisories/GHSA-hjq6-52gw-2g7p - https://nvd.nist.gov/vuln/detail/CVE-2024-22423 - https://github.com/yt-dlp/yt-dlp/releases/tag/2024.04.09 - https://github.com/yt-dlp/yt-dlp/commit/ff07792676f404ffff6ee61b5638c9dc1a33a37a