Possible Open Redirect in Host Authorization Middleware

There is a possible open redirect vulnerability in the Host Authorization

middleware in Action Pack. This vulnerability has been assigned the CVE

identifier CVE-2021-44528.

Versions Affected: >= 6.0.0.

Not affected: < 6.0.0

Fixed Versions:,, 7.0.0.rc2


Specially crafted “X-Forwarded-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 << '.EXAMPLE.com'

When an allowed host contains a leading dot, a specially crafted Host header

can be used to redirect to a malicious website.

This vulnerability is similar to CVE-2021-22881 and CVE-2021-22942.


The fixed releases are available at the normal locations.


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-authorzation-open-redirect.patch - Patch for 6.0 series

  • 6-1-host-authorzation-open-redirect.patch - Patch for 6.1 series

  • 7-0-host-authorzation-open-redirect.patch - Patch for 7.0 series

Please note that only the 6.1.Z, 6.0.Z, and 5.2.Z 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 @krynos for originally

reporting this!

Huge thanks to

@stefschenkelaars for

writing a patch along with tests to fix this issue!

6-0-host-authorzation-open-redirect.patch (5.9 KB) 6-1-host-authorzation-open-redirect.patch (6.0 KB) 7-0-host-authorzation-open-redirect.patch (6.0 KB)