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
<script type="application/ld+json">
{
"@context": "https://schema.org",
"@type": "VideoObject",
"name": "ffmpeg",
"encodingFormat": "video/exe",
"contentUrl": "https://example.com/video.mp4"
}
</script>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
Summary
yt-dlpdoes not limit the extensions of downloaded files, which could lead to arbitrary filenames being created in the download folder (and path traversal on Windows). Sinceyt-dlpalso 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-dlpversion 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)sat 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:
--ies default,-generic)-o "%(title)s [%(id)s].%(ext)s)--write-subs,--write-auto-subs,--all-subs,--write-srt)--ignore-config --config-location ...to not load config from common locationsDetails
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
this will try and download a file called
ffmpeg.exe(-o "%(title)s.%(ext)s).ffmpeg.exewill 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.confto 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