Debian: DSA-4687-1 Critical: Exim4 Authentication Bypass

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 the oldstable distribution (stretch), this problem has been fixed
in version 4.89-2+deb9u7.

For the stable distribution (buster), this problem has been fixed in
version 4.92-8+deb10u4.

We recommend that you upgrade your exim4 packages.

For the detailed security status of exim4 please refer to
its security tracker page at:
https://security-tracker.debian.org/tracker/source-package/exim4

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