yt-dlp File Downloader cookie leak

Impact

During file downloads, yt-dlp or the external downloaders that yt-dlp employs may leak cookies on HTTP redirects to a different host, or leak them when the host for download fragments differs from their parent manifest's host.

This vulnerable behavior is present in all versions of youtube-dl, youtube-dlc and yt-dlp released since 2015.01.25. All native and external downloaders are affected, except for curl and httpie (httpie version 3.1.0 or later).

At the file download stage, all cookies are passed by yt-dlp to the file downloader as a Cookie header, thereby losing their scope. This also occurs in yt-dlp's info JSON output, which may be used by external tools. As a result, the downloader or external tool may indiscriminately send cookies with requests to domains or paths for which the cookies are not scoped.

An example of a potential attack scenario exploiting this vulnerability:

1. an attacker has crafted a malicious website with an embedded URL designed to be detected by yt-dlp as a video download. This embedded URL has the domain of a trusted site that the user has loaded cookies for, and conducts an unvalidated redirect to a target URL.
2. yt-dlp extracts this URL and calculates a Cookie header based on its domain for the file downloader to make its request(s) with.
3. the download URL redirects to a server controlled by the attacker, to which yt-dlp forwards the user's sensitive cookie information.

Patches

yt-dlp version 2023.07.06 fixes this issue by doing the following:

• Remove the Cookie header upon HTTP redirects
• Have native downloaders calculate their own Cookie header from the cookiejar
• Utilize external downloaders' built-in support for cookies instead of passing them as header arguments
• If the external downloader does not have proper cookie support, then disable HTTP redirection (axel only)
• Process cookies passed as HTTP headers to limit their scope (--add-header "Cookie:..." is scoped to input URL domain only)
• Store cookies in a separate cookies field of the info dict instead of http_headers so as not to lose their scope

Patches for youtube-dl are expected and we will update this advisory when they are merged.

Workarounds

It is recommended to upgrade yt-dlp to version 2023.07.06 as soon as possible.

For users who are not able to upgrade:

• Avoid using cookies and user authentication methods (--cookies, --cookies-from-browser, --username, --password, --netrc). While extractors may set custom cookies, these usually do not contain sensitive information.
• Avoid using --load-info-json

Or, if authentication is a must:

• Verify the integrity of download links from unknown sources in browser (including redirects) before passing them to yt-dlp
• Use curl as external downloader, since it is not impacted (--downloader curl)
• Avoid fragmented formats such as HLS/m3u8, DASH/mpd and ISM (use -f "(bv*+ba/b)[protocol~='^https?$']")

References

• https://github.com/yt-dlp/yt-dlp/security/advisories/GHSA-v8mc-9377-rwjj
• https://nvd.nist.gov/vuln/detail/CVE-2023-35934
• https://github.com/yt-dlp/yt-dlp/releases/tag/2023.07.06
• https://github.com/yt-dlp/yt-dlp-nightly-builds/releases/tag/2023.07.06.185519
• https://github.com/yt-dlp/yt-dlp/commit/1ceb657bdd254ad961489e5060f2ccc7d556b729
• https://github.com/yt-dlp/yt-dlp/commit/f8b4bcc0a791274223723488bfbfc23ea3276641
• https://github.com/yt-dlp/yt-dlp/commit/3121512228487c9c690d3d39bfd2579addf96e07