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Fencer Vulns
critical 9.8

CVE-2018-6789 kev+ ransomware in the critical feed json

An issue was discovered in the base64d function in the SMTP listener in Exim before 4.90.1.

published 2018-02-08 8 y ago modified 2026-06-17 4 mo ago also EUVD-2018-18536

cvss
9.8
version 3.1, CNA
cisa kev
Exploited
added 2021-11-03, used in ransomware
epss
82.1%
EPSS 82.1% chance of exploitation in 30 days, percentile 99.6%
public exploits
2
Exploit-DB

Summary

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.

Patch / fix

cisa required action Apply updates per vendor instructions.

  • exim exim 4.90.1
  • exim4 Debian 14, Debian 13, Debian 12 4.90.1-1

debian advisories DEBIAN-CVE-2018-6789

  • exim4 Ubuntu 14.04 LTS 4.82-3ubuntu2.4
  • exim4 Ubuntu 16.04 LTS 4.86.2-2ubuntu2.3

ubuntu advisories UBUNTU-CVE-2018-6789

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • exim openSUSE Tumbleweed 4.94.2-4.2
  • exim Package Hub 15 SP2 4.94.2-bp152.6.4.1
  • libspf2 Package Hub 15 SP2 1.2.10-bp152.5.1
  • exim Package Hub 15 SP1 4.94.2-bp151.2.4.1
  • libspf2 Package Hub 15 SP1 1.2.10-bp151.4.1
  • exim openSUSE Leap 15.2 4.94.2-lp152.8.3.1

opensuse advisories openSUSE-SU-2024:10746-1openSUSE-SU-2021:0754-1openSUSE-SU-2021:0753-1openSUSE-SU-2021:0677-1

  • exim Alpine 3.24, Alpine 3.23, Alpine 3.22 +15 more 4.90.1-r0

alpine advisories ALPINE-CVE-2018-6789

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • exim Arch Linux 4.90.1-1

arch linux advisories AVG-608

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2018-6789 updated cvss 8.1

exim: buffer overflow in b64decode() function, possibly leading to remote code execution

  • Red Hat Enterprise Linux 5 exim
    affected: no fix planned “Will not fix”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Timeline

  1. Published
  2. First public exploit (EDB-44571)
  3. Added to CISA KEV
  4. CISA patch deadline
  5. CISA SSVC: exploitation active

Known exploited

Added
5 y ago
Patch by
2022-05-03 (4 y ago)
Ransomware
Known to be used in ransomware campaigns
Required action
Apply updates per vendor instructions.
Vendor, product
Exim, Exim
CISA name
Exim Buffer Overflow Vulnerability

ATT&CK techniques

How it is exploited and what it leads to, in MITRE ATT&CK terms.

  • T1190 Exploit Public-Facing Application exploitation
  • T1059 Command and Scripting Interpreter primary impact

kev release 2025-07-28, att&ck v16.1. KEV to ATT&CK mappings by the MITRE Center for Threat-Informed Defense (Mappings Explorer, Apache-2.0). © 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation. Terms of use

CISA SSVC

Exploitation
Active, exploited in the wild
Automatable
yes
Technical impact
total
Assessed
21 mo ago

Exploit prediction

82.14% chance of exploitation in the next 30 days, higher than 99.6% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • EDB-45671 exim 4.90 - Remote Code Execution remote, 2018-10-24
  • EDB-44571 Exim < 4.90.1 - 'base64d' Remote Code Execution remote, 2018-05-02
  • devco.re https://devco.re/blog/2018/03/06/exim-off-by-one-RCE-exploiting-CVE-2018-6789-en/ referenced PoC, tagged "exploit" by a source, unverified
  • packetstormsecurity.com http://packetstormsecurity.com/files/162959/Exim-base64d-Buffer-Overflow.html referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

Classification

Weakness
  • CWE-120 Buffer Copy without Checking Size of Input

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.