CyberSecBulletin
CVE-2023-35934NVD status: Modified

yt-dlp: URL Redirection to Untrusted Site

Published Updated By the CyberSecBulletin desk

CVE-2023-35934 is a high-severity URL redirection to untrusted site vulnerability in yt-dlp, with a CVSS 3.1 base score of 8.2 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. Affected yt-dlp versions: yt-dlp < 2023.07.06; yt-dlp < nightly 2023.07.06.185519. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.05% chance of exploitation within 30 days, higher than 65% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Check which version of yt-dlp you run against the affected versions below, and install the vendor's latest release.
  2. Read the advisory on github.com for workarounds and exact fixed builds.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
  4. Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.

Affected products and versions

VendorProductAffected versionsFixed in
Yt-dlpyt-dlpyt-dlp < 2023.07.06; yt-dlp < nightly 2023.07.06.185519Not stated
Youtube-dlc ProjectYoutube-dlcNot specified in the recordNot stated
Yt-dlYoutube-dl2015.01.25 and laterNot stated
Fedora ProjectFedora37; 38Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
RequiredA user must take an action such as opening a file or link.
Scope
ChangedThe attack can reach beyond the vulnerable component into other systems.
Confidentiality
HighAll data handled by the component can be read.
Integrity
LowLimited modification of data is possible.
Availability
NoneAvailability is not affected.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.16.1MediumCNA (github.com)
CVSS 3.18.2HighNVD

Official 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: URL Redirection to Untrusted Site

The web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect.

How developers prevent this class of flaw

  • Use an intermediate disclaimer page that provides the user with a clear warning that they are leaving the current site. Implement a long timeout before the redirect occurs, or force the user to click on the link. Be careful to avoid XSS problems (CWE-79) when generating the disclaimer page.
  • When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs. For example, ID 1 could map to /login.asp and ID 2 could map to http://www.example.com/. Features such as the ESAPI AccessReferenceMap provide this capability.
  • Ensure that no externally-supplied requests are honored by requiring that all redirect requests include a unique nonce generated by the application. Be sure that the nonce is not predictable (CWE-330).

More URL Redirection to Untrusted Site vulnerabilities (CWE-601)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in yt-dlp

All yt-dlp vulnerabilities

Recent URL Redirection to Untrusted Site vulnerabilities

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