Known exploited · Exim

CVE-2018-6789: Exim Buffer Overflow Vulnerability

What it is

Exim contains a buffer overflow vulnerability in the base64d function part of the SMTP listener that may allow for remote code execution.

Added November 3, 2021Due May 3, 2022CISA KEV catalog 2026.10.01

Vendor: Exim
Product: Exim
Added to KEV: November 3, 2021
CISA due date: May 3, 2022
Ransomware use: Known
Weakness: CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer

What CISA requires

Apply updates per vendor instructions.

Find every instance of Exim you run, including the forgotten ones, and check its version against the vendor advisory.
Apply the vendor's fix or mitigation, before May 3, 2022 if you are bound by CISA's deadline, sooner if it faces the internet.
Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.

H2 Security

We check where you run it, patch or mitigate with your team, and look for signs it was already used against you.

T Academy

Security engineering on real hosts in the browser, every objective checked on the machine. The first two lessons of Linux 1 are free.

Source: CISA Known Exploited Vulnerabilities Catalog (public domain), catalog version 2026.10.01.