Exploited. On CISA's list since 2021-11-03, and used by ransomware.
Exim Buffer Overflow Vulnerability
CVE-2018-6789 · Exim Exim · Published 2018-02-08
How bad would it be?
9.8 out of 10
CVSS rates it critical: about as damaging as flaws get.
How likely is it to be used?
82%
Estimated chance of exploitation in the next 30 days, among the top 1% of all scored flaws (EPSS, 2026-10-29).
Is it already being used?
Yes
CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 1641 days ago (2022-05-03).
What CISA says to do
Apply updates per vendor instructions.
Exim contains a buffer overflow vulnerability in the base64d function part of the SMTP listener that may allow for remote code execution.
What the flaw is
An issue was discovered in the base64d function in the SMTP listener in Exim before 4.90.1. By sending a handcrafted message, a buffer overflow may happen. This can be used to execute code remotely.
From the NVD.
Fixes and advisories
Learn this
Explore this week’s weaknesses and all learning topics
Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.
CWE-119 · CISA KEV. We have not selected a close learning match for this label.
CWE-120 · NVD record: 134c704f-9b21-4f2e-91b3-4a467353bcc0; NVD record: nvd@nist.gov. We have not selected a close learning match for this label.
CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.
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Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.