CVE-2023-40581

yt-dlp –exec shell command remote code execution

• CVSS 7.8
• CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
• Input Validation and Sanitization
• Remote

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 version 2021.04.11. yt-dlp version 2023.09.24 fixes this issue by properly escaping each special character. `\n` will be replaced by `\r` as no way of escaping it has been found. It is recommended to upgrade yt-dlp to version 2023.09.24 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: 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.

CVE

CVE-2023-40581

CWE

CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

CVSS base score

7.8

Published

2023-09-25

OWASP

A03 Injection

Orthogonal defect classification

Build/Package/Merge

Code defect classification

Packaging Issues

Category

Input Validation and Sanitization

Subcategory

Command Injection

Accessibility scope

Remote

Impact

Arbitrary Code Execution

Fixed by upgrading

Yes

Solution

Update to yt-dlp version 2023.09.24 or higher

import subprocess

def modified_exec(command, metadata):
    """Vulnerable function that demonstrates the security issue."""
    command_to_run = command.format(**metadata)

    subprocess.run(command_to_run, shell=True)

metadata = {
    'filepath': 'example.mp4',
    'title': 'example title with & special chars',
}

command = 'echo {title} > {filepath}'

modified_exec(command, metadata)

import subprocess
import shlex

def modified_exec(command, metadata):
    """Secure function that fixes the vulnerability."""
    
    sanitized_metadata = {key: value.replace('\n', '\r') for key, value in metadata.items()}
    
    modified_command = command.format(**sanitized_metadata)
    modified_command = shlex.quote(modified_command)

    subprocess.run(modified_command, shell=True)

metadata = {
    'filepath': 'example.mp4',
    'title': 'example title with & special chars',
}

command = 'echo {title} > {filepath}'

modified_exec(command, metadata)

@misc{vaitp:cve202340581,
  title        = {{yt-dlp --exec shell command remote code execution}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2023},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2023-40581},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2023-40581/}}
}