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Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')


Severity High
Score 7.8/10


yt-dlp is a youtube-dl fork with additional features and fixes. yt-dlp allows the user to provide shell command lines to be executed at various stages in its download steps through the "--exec" flag. This flag allows output template expansion in its argument, so that metadata values may be used in the shell commands. The metadata fields can be combined with the "%q" conversion, which is intended to quote/escape these values so they can be safely passed to the shell. However, the escaping used for "cmd" (the shell used by Python's "subprocess" on Windows) does not properly escape special characters, which can allow for remote code execution if "--exec" is used directly with maliciously crafted remote data. This vulnerability only impacts "yt-dlp" on Windows, and the vulnerability is present regardless of whether "yt-dlp" is run from "cmd" or from "PowerShell". Support for output template expansion in "--exec", along with this vulnerable behavior, was added to "yt-dlp" in versions 2021.04.11 prior to 2023.09.24. This issue was fixed by properly escaping each special character. "\n" will be replaced by "\r" as no way of escaping it has been found. 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: 1. Avoid using any output template expansion in --exec other than {} (filepath). 2. If expansion in --exec is needed, verify the fields you are using do not contain ", | or &. 3. Instead of using "--exec", write the info json and load the fields from it instead.

  • LOW
  • HIGH
  • NONE
  • HIGH
  • HIGH

CWE-78 - OS Command Injection

The OS command injection weakness (also known as shell injection) is a vulnerability which enables an attacker to run arbitrary OS commands on a server. This is done by modifying the intended downstream OS command and injecting arbitrary commands, enabling the execution of unauthorized OS commands. This has the potential to fully compromise the application along with all of its data, and, if the compromised process does not follow the principle of least privileges, it may compromise other parts of the hosting infrastructure as well. This weakness is listed as number ten in the 'CWE Top 25 Most Dangerous Software Weaknesses'.

Advisory Timeline

  • Published