A critical vulnerability affects hundreds of thousands of email servers. The bug is a vulnerability in Exim, a mail transfer agent that relays emails from senders to recipients. A Taiwanese security researcher named Meh Chang discovered the bug, which he reported to the Exim crew on February 2. The Exim team released Exim distribution 4.90.1 on February 10 that fixes the RCE issue. There is no public exploit code for taking advantage of vulnerable Exim servers, but this will change in the days following Chang’s blog post.
Source: https://www.bleepingcomputer.com/news/security/vulnerability-affects-half-of-the-internets-email-servers/