[CVE-2019-5420] Possible Remote Code Execution Exploit in Rails Development Mode

[Aaron Patterson]

There is a possible a possible remote code executing exploit in Rails when in
development mode. This vulnerability has been assigned the CVE identifier
CVE-2019-5420.

Versions Affected: 6.0.0.X, 5.2.X.
Not affected: None.
Fixed Versions: 6.0.0.beta3, 5.2.2.1

Impact
------
With some knowledge of a target application it is possible for an attacker to
guess the automatically generated development mode secret token. This secret
token can be used in combination with other Rails internals to escalate to a
remote code execution exploit.

All users running an affected release should either upgrade or use one of the
workarounds immediately.

Releases
--------
The 6.0.0.beta3 and 5.2.2.1 releases are available at the normal locations.

Workarounds
-----------
This issue can be mitigated by specifying a secret key in development mode.
In "config/environments/development.rb" add this:

config.secret_key_base = SecureRandom.hex(64)


Patches
-------
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-railties-dev-mode-token.patch - Patch for 6.0 series
* 5-2-railties-dev-mode-token.patch - Patch for 5.2 series

Please note that only the 5.2.x, 5.1.x, 5.0.x, and 4.2.x 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.

Credits
-------
Thanks to ooooooo_q

--
Aaron Patterson
http://tenderlovemaking.com/