---
id: "CVE-2019-16928"
kind: "vulnerability"
aliases: ["CVE-2019-16928"]
title: "Exim Exim Internet Mailer: Exim Out-of-bounds Write Vulnerability"
severity: "critical"
cvss: 9.8
epss: 0.41638
exploited: true
status: "open"
category: "package"
products: [{"name": "Exim Exim Internet Mailer", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exim", "exploited", "mail-server", "package", "self-hosted"]
not_affected_if: ["managed-hosting", "no-exim-installed"]
published_at: "2019-09-27T21:15:10+00:00"
first_seen_at: "2026-10-23T19:11:52+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-2019-16928", "first_seen_at": "2026-10-23T19:11:52+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2019-16928", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2019-16928", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Exim Exim Internet Mailer: Exim Out-of-bounds Write Vulnerability

Exim, a widely used mail transfer agent, has an out-of-bounds write in its EHLO/string handling that lets a remote sender write past a buffer. An attacker who can reach the SMTP port can run code on the mail server, and CISA lists it as actively exploited.

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

## Affected

- vendor:Exim Exim Internet Mailer affected ? fixed ?

## How to check

Run exim -bV to read the installed version and compare it with the fixed release in the vendor advisory.
See whether port 25 on the host accepts SMTP connections from the internet.

## Fix

Upgrade Exim to a release that includes the vendor fix for CVE-2019-16928, following the vendor instructions named in the CISA entry.

## Timeline

- 2026-10-23T19:11:52+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2019-16928
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2019-16928
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2019-16928

## From the sources

Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in string_vformat in string.c involving a long EHLO command.

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