It was discovered that exim4, a mail transport agent, suffers from a authentication bypass vulnerability in the spa authentication driver. The spa authentication driver is not enabled by default.

For Debian 8 Jessie, this problem has been fixed in version 4.84.2-2+deb8u7.

We recommend that you upgrade your exim4 packages.

Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: https://wiki.debian.org/LTS