There is a possible open redirect vulnerability in the Host Authorization middleware in Action Pack. This vulnerability has been assigned the CVE identifier CVE-2021-22881.
Versions Affected: >= 6.0.0
Not affected: < 6.0.0
Fixed Versions: 220.127.116.11, 18.104.22.168
Specially crafted “Host” headers in combination with certain “allowed host” formats can cause the Host Authorization middleware in Action Pack to redirect users to a malicious website.
Impacted applications will have allowed hosts with a leading dot. For example, configuration files that look like this:
config.hosts << '.tkte.ch'
When an allowed host contains a leading dot, a specially crafted Host header can be used to redirect to a malicious website.
The fixed releases are available at the normal locations.
In the case a patch can’t be applied, the following monkey patch can be used in an initializer:
module ActionDispatch class HostAuthorization private def authorized?(request) valid_host = / \A (?<host>[a-z0-9.-]+|\[[a-f0-9]*:[a-f0-9\.:]+\]) (:\d+)? \z /x origin_host = valid_host.match( request.get_header("HTTP_HOST").to_s.downcase) forwarded_host = valid_host.match( request.x_forwarded_host.to_s.split(/,\s?/).last) origin_host && @permissions.allows?(origin_host[:host]) && ( forwarded_host.nil? || @permissions.allows?(forwarded_host[:host])) end end end
To aid users who aren’t able to upgrade immediately we have provided patches for the two supported release series. They are in git-am format and consist of a single changeset.
- 6-0-host-authorization-open-redirect.patch (2.5 KB)
- 6-1-host-authorization-open-redirect.patch (2.6 KB)
Please note that only the 5.2, 6.0, and 6.1 series are supported at present. Users of earlier unsupported releases are advised to upgrade as soon as possible as we cannot guarantee the continued availability of security fixes for unsupported releases.
Thanks to @tktech (HackerOne) for reporting this issue!