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A remote code execution vulnerability exists in Exim versions between 4.70 and 4.80, inclusive. Exim is the mail transfer agent used by cPanel & WHM.

Security Rating
This vulnerability has been rated as Critical [1] by the cPanel Security team.

Description

A remote code execution flaw in Exim has been discovered by an internal audit performed by the Exim developers [2]. This vulnerability may lead to arbitrary code execution with the privileges of the user executing the Exim daemon. In some circumstances this may lead to privilege escalation.

The vulnerability is tied to the DKIM support introduced in Exim 4.70. It has been assigned CVE-2012-5671[3].

The following Exim RPMs, as distributed by cPanel, Inc. are known to be vulnerable:

* exim-4.76-1
* exim-4.77-0
* exim-4.77-1
* exim-4.80-0
* exim-4.80-1

These RPMs were shipped as part of cPanel & WHM versions 11.32 and 11.34.

Solution

Servers that are using the default DKIM verification settings provided with cPanel & WHM 11.32 and newer are not vulnerable. The default settings disable DKIM key verification by adding the following to /etc/exim.conf

warn control = dkim_disable_verify

This prevents the exploitable code from being available during exim execution.

To fully resolve the issue cPanel has produced new Exim RPMs for cPanel & WHM version 11.32 and 11.34. Server Owners are strongly urged to update their cPanel & WHM installations to the following versions:

* cPanel & WHM 11.32.5.13
* cPanel & WHM 11.34.0.6

Exim RPMs are distributed through cPanel’s package management system. All cPanel & WHM servers receiving updates automatically will receive the updated Exim RPM during normal update and maintenance operations (upcp). Servers with automatic updates disabled will require action in order to receive the update. We recommend all customers to update to the latest releases of 11.32 and 11.34 as soon as possible.

Servers who have disabled Exim updates, via the Update Preferences interface in WHM, are strongly urged to re-enable updates.

To perform a manual update of cPanel & WHM, perform the following:

1. Login to your server as root using SSH
2. Execute the following command on the command line:

/scripts/upcp

Updated cPanel & WHM 11.32, and 11.34, servers will have the following Exim RPM:

exim-4.80-3

References

[1] http://docs.cpanel.net/twiki/bin/view/AllDocumentation/SecurityLevels
[2] https://lists.exim.org/lurker/message/20121026.080330.74b9147b.en.html
[3] http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-5671