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yt-dlp: `--exec` command injection when using `%q` in yt-dlp on Windows (Bypass of CVE-2023-40581)

High severity GitHub Reviewed Published Apr 9, 2024 in yt-dlp/yt-dlp • Updated Apr 20, 2024

Package

pip yt-dlp (pip)

Affected versions

>= 2021.04.11, < 2024.04.09

Patched versions

2024.04.09

Description

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.

> 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.
yt_dlp/compat/__init__.py line 31-33

    def compat_shlex_quote(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:

%CMDCMDLINE:~-1%&calc.exe

References

References

@Grub4K Grub4K published to yt-dlp/yt-dlp Apr 9, 2024
Published by the National Vulnerability Database Apr 9, 2024
Published to the GitHub Advisory Database Apr 10, 2024
Reviewed Apr 10, 2024
Last updated Apr 20, 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
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Changed
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:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H

EPSS score

0.045%
(17th percentile)

Weaknesses

CVE ID

CVE-2024-22423

GHSA ID

GHSA-hjq6-52gw-2g7p

Source code

Credits

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