CVE-2018-6789

Exim is a program many servers use to send and receive email. This bug is like a mistake in how Exim decodes “base64” text inside an email: a crafted message can overwhelm the program and let an attacker take control of the server. The impact can range from the mail server being knocked offline to attackers running code on your system.

This matters if your business runs an Exim-based email server (or a server that uses Exim for SMTP handling), including Debian, Ubuntu, and Astra Linux installations. It is especially important because the weakness is reachable over the network without needing a username or password, so exposure depends mainly on whether your SMTP listener is reachable from the attacker. If your SMTP port isn’t reachable from the internet and is only accessible to trusted internal systems, the risk is lower—but if it is exposed, treat it as high risk.

This is a RED issue because attackers can exploit it remotely without authentication, and it is confirmed to have been used in ransomware campaigns (CISA KEV listing). With public exploits available, delay materially increases the chance of compromise. Apply the fix immediately—upgrade Exim to the fixed version.