---
id: "CVE-2018-6789"
kind: "vulnerability"
aliases: ["CVE-2018-6789"]
title: "Exim Exim: Exim Buffer Overflow Vulnerability"
severity: "critical"
cvss: 9.8
epss: 0.82137
exploited: true
status: "open"
category: "package"
products: [{"name": "Exim Exim", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exim", "exploited", "mail-server", "package", "ransomware", "self-hosted"]
not_affected_if: ["managed-mail-service"]
published_at: "2018-02-08T23:29:01+00:00"
first_seen_at: "2026-10-23T19:11:53+00:00"
updated_at: "2026-10-23T21:57:35+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2018-6789", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2018-6789", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2018-6789", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Exim Exim: Exim Buffer Overflow Vulnerability

Exim's SMTP listener has a buffer overflow in its base64d function, which an unauthenticated remote sender can trigger. The flaw may allow remote code execution on the mail server.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Exim Exim affected ? fixed ?

## How to check

Run exim -bV to see the installed version and compare it with the fixed release in the vendor advisory.

## Fix

Upgrade Exim to a release that includes the vendor fix; CISA directs federal users to apply the vendor update.

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2018-6789
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2018-6789
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2018-6789

## From the sources

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

CISA required action: Apply updates per vendor instructions.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_