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

Open Source Vulnerabilities CVE-2024-22423

yt-dlp is a youtube-dl fork with additional features and fixes. 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 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. 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 `&`; and/or instead of using `--exec`, write the info json and load the fields from it instead.

Open Source Vulnerabilities GHSA-hjq6-52gw-2g7p

### Summary The [patch that addressed CVE-2023-40581](https://github.com/yt-dlp/yt-dlp/commit/de015e930747165dbb8fcd360f8775fd973b7d6e) 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](https://github.com/yt-dlp/yt-dlp/releases/tag/2021.04.11). ```cmd > 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](https://github.com/yt-dlp/yt-dlp/blob/8e6e3651727b0b85764857fc6329fe5e0a3f00de/yt_dlp/compat/__init__.py#L31-L33) ```python 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: ```cmd %CMDCMDLINE:~-1%&calc.exe ``` ### References - https://github.com/yt-dlp/yt-dlp/security/advisories/GHSA-hjq6-52gw-2g7p - https://nvd.nist.gov/vuln/detail/CVE-2024-22423 - https://github.com/yt-dlp/yt-dlp/releases/tag/2024.04.09 - https://github.com/yt-dlp/yt-dlp/commit/ff07792676f404ffff6ee61b5638c9dc1a33a37a

Open Source Vulnerabilities PYSEC-2026-2066

### Summary The [patch that addressed CVE-2023-40581](https://github.com/yt-dlp/yt-dlp/commit/de015e930747165dbb8fcd360f8775fd973b7d6e) 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](https://github.com/yt-dlp/yt-dlp/releases/tag/2021.04.11). ```cmd > 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](https://github.com/yt-dlp/yt-dlp/blob/8e6e3651727b0b85764857fc6329fe5e0a3f00de/yt_dlp/compat/__init__.py#L31-L33) ```python 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: ```cmd %CMDCMDLINE:~-1%&calc.exe ``` ### References - https://github.com/yt-dlp/yt-dlp/security/advisories/GHSA-hjq6-52gw-2g7p - https://nvd.nist.gov/vuln/detail/CVE-2024-22423 - https://github.com/yt-dlp/yt-dlp/releases/tag/2024.04.09 - https://github.com/yt-dlp/yt-dlp/commit/ff07792676f404ffff6ee61b5638c9dc1a33a37a