GHSA-79w7-vh3h-8g4j yt-dlp File system modification and RCE through improper file-extension sanitization

• PyPI yt-dlp: < 2024.07.01 → fixed in 2024.07.01

Summary `yt-dlp` 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). Since `yt-dlp` also reads config from the working directory (and on Windows executables will be executed from the yt-dlp directory) this could lead to arbitrary code being executed. Patches `yt-dlp` version 2024.07.01 fixes this issue by whitelisting the allowed extensions. This means some very uncommon extensions might not get downloaded; however, it will also limit the possible exploitation surface. Workarounds It is recommended to upgrade yt-dlp to version 2024.07.01 as soon as possible, always have `.%(ext)s` at the end of the output template, and make sure you trust the websites that you are downloading from. Also, make sure to never download to a directory within PATH or other sensitive locations like your user directory, `system32`, or other binaries locations. For users not able to upgrade: • Make sure the extension of the media to download is a common video/audio/sub/... one • Try to avoid the generic extractor (`--ies default,-generic`) • Keep the default output template (`-o "%(title)s [%(id)s].%(ext)s`) • Omit any of the subtitle options (`--write-subs`, `--write-auto-subs`, `--all-subs`, `--write-srt`) • Use `--ignore-config --config-location ...` to not load config from common locations Details One potential exploitation might look like this: From a mimetype we do not know, we default to trimming the leading bit and using the remainder. Given a webpage that contains ```html { "@context": "https://schema.org", "@type": "VideoObject", "name": "ffmpeg", "encodingFormat": "video/exe", "contentUrl": "https://example.com/video.mp4" } ``` this will try and download a file called `ffmpeg.exe` (`-o "%(title)s.%(ext)s`). `ffmpeg.exe` will be searched for in the current directory, and so upon the next run arbitrary code can be executed. Alternatively, when engineering a file called `yt-dlp.conf` to be created, the config file could contain `--exec ...` and so would also execute arbitrary code. Acknowledgement A big thanks to @JarLob for independently finding a new application of the same underlying issue. More can be read about on the dedicated GitHub Security Lab disclosure here: Path traversal saving subtitles (GHSL-2024-090) References • https://github.com/yt-dlp/yt-dlp/security/advisories/GHSA-79w7-vh3h-8g4j • https://nvd.nist.gov/vuln/detail/CVE-2024-38519 • https://github.com/yt-dlp/yt-dlp/releases/tag/2024.07.01 • https://github.com/yt-dlp/yt-dlp/commit/5ce582448ececb8d9c30c8c31f58330090ced03a • https://securitylab.github.com/advisories/GHSL-2024-090_yt-dlp