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:
- 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.
- yt-dlp extracts this URL and calculates a
Cookie header based on its domain for the file downloader to make its request(s) with.
- 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
NVD description
yt-dlp is a command-line program to download videos from video sites. 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 yt-dlp prior to 2023.07.06 and nightly 2023.07.06.185519. All native and external downloaders are affected, except for `curl` and `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.
yt-dlp version 2023.07.06 and nightly 2023.07.06.185519 fix this issue by removing the `Cookie` header upon HTTP redirects; having native downloaders calculate the `Cookie` header from the cookiejar, utilizing external downloaders' built-in support for cookies instead of passing them as header arguments, disabling HTTP redirectiong if the external downloader does not have proper cookie support, processing cookies passed as HTTP headers to limit their scope, and having a separate field for cookies in the info dict storing more information about scoping
Some workarounds are available for those who are unable to upgrade. Avoid using cookies and user authentication methods. While extractors may set custom cookies, these usually do not contain sensitive information. Alternatively, 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; and/or avoid fragmented formats such as HLS/m3u8, DASH/mpd and ISM.