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yt-dlp File system modification and RCE through improper file-extension sanitization

High severity GitHub Reviewed Published Jul 1, 2024 in yt-dlp/yt-dlp • Updated Jul 5, 2024

Package

pip yt-dlp (pip)

Affected versions

< 2024.07.01

Patched versions

2024.07.01

Description

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

References

@bashonly bashonly published to yt-dlp/yt-dlp Jul 1, 2024
Published by the National Vulnerability Database Jul 2, 2024
Published to the GitHub Advisory Database Jul 2, 2024
Reviewed Jul 2, 2024
Last updated Jul 5, 2024

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS score

0.044%
(14th percentile)

CVE ID

CVE-2024-38519

GHSA ID

GHSA-79w7-vh3h-8g4j

Source code

Credits

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