CVE-2026-40295: Devise: Open Redirect via Unvalidated `request.referrer` in Timeoutable Session Timeout Handler

Summary

When the Timeoutable module is enabled in Devise, the FailureApp#redirecturl method returns request.referrer — the HTTP Referer header, which is attacker-controllable — without validation for any non-GET request that results in a session timeout. An attacker who hosts a page with an auto-submitting cross-origin form can cause a victim with an expired Devise session to be redirected to an arbitrary external URL. This contrasts with the GET timeout path (which uses server-side attemptedpath) and Devise's own storelocationfor mechanism (which strips external hosts via extractpathfromlocation), both of which are protected; only the non-GET timeout redirect path is unprotected.

Details

The vulnerable code is in lib/devise/failureapp.rb:

ruby def redirecturl if wardenmessage == :timeout flash[:timedout] = true if isflashingformat?

path = if request.get? attemptedpath # safe: server-side value from warden options else request.referrer # UNSAFE: HTTP Referer header, attacker-controlled end

path || scopeurl else scopeurl end end

This is passed directly to redirectto:

ruby def redirect storelocation! # ... redirectto redirecturl # redirecturl may be an external attacker URL end

The GET timeout path uses attemptedpath, which is set server-side by Warden and cannot be influenced by the client. The storelocation! method also only runs for GET requests, so no session-based protection is applied on POST timeouts.

By contrast, Devise's storelocationfor method (used elsewhere) correctly sanitizes URLs via extractpathfromlocation, which strips the scheme and host.

Impact

- Victims with expired sessions who click any attacker-crafted link or visit an attacker page with an auto-submitting form are redirected to an arbitrary external URL. - The redirect happens transparently via a trusted domain (the target app's domain), bypassing browser phishing warnings. - An attacker can redirect victims to a fake login page to harvest credentials (phishing), or to malicious download sites.

Note: Rails' built-in open-redirect protection does not mitigate this issue. Devise::FailureApp is an ActionController::Metal app with its own isolated copy of the relevant redirect configuration, so config.actioncontroller.actiononopenredirect = :raise (and the older raiseonopenredirects setting) do not reach it.

Patches

This is patched in Devise v5.0.4. Users should upgrade as soon as possible.

Workaround

None beyond upgrading. If an upgrade is not immediately possible, the same changes from the patch commit can be applied as a monkey-patch in a Rails initializer (Devise::FailureApp#redirecturl and Devise::Controllers::StoreLocation#extractpathfromlocation). Remove the monkey-patch after upgrading.