CVE-2018-6789: Exim Buffer Overflow Vulnerability

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: yes — in CISA KEV since 2021-11-03
EPSS: 82.1% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2018-02-08 · updated 2026-06-17
Weakness: CWE-120

Description

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.

Affected products

Canonical Ubuntu Linux: 14.04, 16.04, 17.10
Debian Linux: 7.0, 8.0, 9.0
Exim: before 4.90.1 — fixed in 4.90.1

How to fix

Upgrade to a fixed version: Exim 4.90.1. Check the vendor advisory for mitigations.

References

http://openwall.com/lists/oss-security/2018/02/10/2
http://packetstormsecurity.com/files/162959/Exim-base64d-Buffer-Overflow.html
http://www.openwall.com/lists/oss-security/2018/02/07/2
http://www.securityfocus.com/bid/103049
http://www.securitytracker.com/id/1040461
https://devco.re/blog/2018/03/06/exim-off-by-one-RCE-exploiting-CVE-2018-6789-en/
https://exim.org/static/doc/security/CVE-2018-6789.txt
https://git.exim.org/exim.git/commit/cf3cd306062a08969c41a1cdd32c6855f1abecf1
https://lists.debian.org/debian-lts-announce/2018/02/msg00009.html
https://usn.ubuntu.com/3565-1/
https://www.debian.org/security/2018/dsa-4110
https://www.exploit-db.com/exploits/44571/

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