[CVE-2020-8167] CSRF Vulnerability in rails-ujs

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Aaron Patterson

May 18, 2020, 11:58:47 AM5/18/20
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CSRF Vulnerability in rails-ujs

There is an vulnerability in rails-ujs that allows attackers to send
CSRF tokens to wrong domains.
This vulnerability has been assigned the CVE identifier CVE-2020-8167.

Versions Affected: rails <= 6.0.3
Not affected: Applications which don't use rails-ujs.
Fixed Versions: rails >=, rails >=


This is a regression of CVE-2015-1840.

In the scenario where an attacker might be able to control the href attribute of an anchor tag or
the action attribute of a form tag that will trigger a POST action, the attacker can set the
href or action to a cross-origin URL, and the CSRF token will be sent.

The FIXED releases are available at the normal locations.


To work around this problem, change code that allows users to control the href attribute of an anchor
tag or the action attribute of a form tag to filter the user parameters.

For example, code like this:

link_to params

to code like this:

link_to filtered_params

def filtered_params
# Filter just the parameters that you trust

To aid users who aren't able to upgrade immediately we have provided patches for the
supported release series. They are in git-am format and consist of a single changeset.

* 5-2-rails-ujs.patch - Patch for 5.2 series
* 6-0-rails-ujs.patch - Patch for 6.0 series


Thanks to Ben Toews of GitHub for reporting the vulnerability to us.
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