USN-2933-1: Exim vulnerabilities

15 March 2016

exim4 vulnerabilities

A security issue affects these releases of Ubuntu and its derivatives:

  • Ubuntu 15.10
  • Ubuntu 14.04 LTS
  • Ubuntu 12.04 LTS

Summary

Several security issues were fixed in Exim.

Software Description

  • exim4 - Exim is a mail transport agent

Details

It was discovered that Exim incorrectly filtered environment variables when used with the perl_startup configuration option. If the perl_startup option was enabled, a local attacker could use this issue to escalate their privileges to the root user. This issue has been fixed by having Exim clean the complete execution environment by default on startup, including any subprocesses such as transports that call other programs. This change in behaviour may break existing installations and can be adjusted by using two new configuration options, keep_environment and add_environment. (CVE-2016-1531)

Patrick William discovered that Exim incorrectly expanded mathematical comparisons twice. A local attacker could possibly use this issue to perform arbitrary file operations as the Exim user. This issue only affected Ubuntu 12.04 LTS and Ubuntu 14.04 LTS. (CVE-2014-2972)

Update instructions

The problem can be corrected by updating your system to the following package versions:

Ubuntu 15.10
exim4-daemon-heavy - 4.86-3ubuntu1.1
exim4-daemon-light - 4.86-3ubuntu1.1
Ubuntu 14.04 LTS
exim4-daemon-custom - 4.82-3ubuntu2.1
exim4-daemon-heavy - 4.82-3ubuntu2.1
exim4-daemon-light - 4.82-3ubuntu2.1
Ubuntu 12.04 LTS
exim4-daemon-custom - 4.76-3ubuntu3.3
exim4-daemon-heavy - 4.76-3ubuntu3.3
exim4-daemon-light - 4.76-3ubuntu3.3

To update your system, please follow these instructions: https://wiki.ubuntu.com/Security/Upgrades.

This update introduces environment filtering, which may break certain existing installations. After performing a standard system update, the new keep_environment and add_environment configurations options can be used to adjust the new behaviour.

References