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Date: Wed, 16 Oct 2013 10:29:41 -0700
From: Aaron Patterson <>
Subject: Possible DoS Vulnerability in Action Mailer (CVE-2013-4389)

Possible DoS Vulnerability in Action Mailer

There is a possible DoS vulnerability in the log subscriber component of
Action Mailer. This vulnerability has been assigned the CVE identifier CVE-2013-4389.

Versions Affected:  3.x.x
Not affected:       4.0.x, 2.3.x
Fixed Versions:     3.2.15

A carefully crafted email address in conjunction with the Action Mailer logger
format string could take advantage of a bug in Ruby's sprintf implementation
and possibly lead to a denial of service attack.

Impacted Ruby code will look something like this:

  "some string #{user_input}" % some_number

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

The FIXED releases are available at the normal locations. 

If you can't upgrade or apply patch to your system, you can work around the
issue by using the following monkey patch after requiring Action Mailer:

module ActionMailer
  class LogSubscriber < ActiveSupport::LogSubscriber
    def deliver(event)
      recipients = Array.wrap(event.payload[:to]).join(', ')
      info("\nSent mail to #{recipients} (#{event.duration.round(1)}ms)")

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. 

* 3-2-log-subscriber.patch - Patch for 3.2 series 
* 3-1-log-subscriber.patch - Patch for 3.1 series 
* 3-0-log-subscriber.patch - Patch for 3.0 series 

Please note that only the 4.0.x, 3.2.x, and 2.3.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.


Thanks to Aaron Neyer for reporting this vulnerability!

Aaron Patterson

View attachment "3-0-log-subscriber.patch" of type "text/plain" (4320 bytes)

View attachment "3-1-log-subscriber.patch" of type "text/plain" (4262 bytes)

View attachment "3-2-log-subscriber.patch" of type "text/plain" (4000 bytes)

Content of type "application/pgp-signature" skipped

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