GHSA-22fp-mf44-f2mq youtube-dl vulnerable to file system modification and RCE through improper file-extension sanitization

• PyPI youtube-dl: >= 2015.01.25, <= 2021.12.17 (no fix yet)

Description This advisory follows the security advisory GHSA-79w7-vh3h-8g4j published by the _yt-dlp/yt-dlp_ project to aid remediation of the issue in the _ytdl-org/youtube-dl_ project. Vulnerability _youtube-dl_ does not limit the extensions of downloaded files, which could lead to arbitrary filenames being created in the download folder (and path traversal on Windows). Impact Since _youtube-dl_ also reads config from the working directory (and, on Windows, executables will be executed from the _youtube-dl_ directory by default) the vulnerability could allow the unwanted execution of local code, including downloads masquerading as, eg, subtitles. Patches The versions of _youtube-dl_ listed as _Patched_ remediate this vulnerability by disallowing path separators and whitelisting allowed extensions. As a result, some very uncommon extensions might not get downloaded. Master code d42a222 or later and nightly builds tagged 2024-07-03 or later contain the remediation. Workarounds Any/all of the below considerations may limit exposure in case it is necessary to use a vulnerable version • have `.%(ext)s` at the end of the output template • download from websites that you trust • do not download to a directory within the executable search `PATH` or other sensitive locations, such as your user directory or system directories • in Windows versions that support it, set `NoDefaultCurrentDirectoryInExePath` to prevent the _cmd_ shell's executable search adding the default directory before `PATH` • consider that the path traversal vulnerability as a result of resolving `non_existent_dir\..\..\target` does not exist in Linux or macOS • ensure the extension of the media to download is a common video/audio/... one (use `--get-filename`) • omit any of the subtitle options (`--write-subs`/` --write-srt`, `--write-auto-subs`/`--write-automatic-subs`, `--all-subs`). References • GHSA-79w7-vh3h-8g4j • https://github.com/ytdl-org/youtube-dl/pull/32830