CVE-2018-6789
CRITICALCISA KEVEPSS 100th pctlDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Exploit Intelligence
Very high risk: more likely to be exploited than 100% of all known CVEs.
Exim Buffer Overflow Vulnerability
Exim contains a buffer overflow vulnerability in the base64d function part of the SMTP listener that may allow for remote code execution.
Apply updates per vendor instructions.
Remediation due: 2022-05-03
Associated with ransomware campaigns
References
Related Vulnerabilities
Other CWE-120 (Classic Buffer Overflow) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2014-0195 | Medium | 6.8 | 100% | - | Fix |
| CVE-2017-7269 | Critical | 9.8 | 100% | KEV | - |
| CVE-2019-11043 | High | 8.7 | 99% | KEV + Ransom | Fix |
| CVE-2011-4862 | High | 10.0 | 95% | - | Fix |
| CVE-2007-5659 | High | 7.8 | 94% | KEV | Fix |
| CVE-2022-3786 | High | 7.5 | 92% | - | Fix |
Common questions
How do I fix CVE-2018-6789?
Published advisories record a fix for 4 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2018-6789 being actively exploited?
Yes. CVE-2018-6789 is listed in the CISA Known Exploited Vulnerabilities catalog, which means exploitation has been observed in the wild. CISA has also linked it to known ransomware campaigns. US federal agencies were required to remediate it by 2022-05-03. Treat it as a priority whatever its CVSS score says.
How severe is CVE-2018-6789?
CVE-2018-6789 has a CVSS v3 base score of 9.8, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2018-6789 affect?
Published advisories record a fix for exim4 (Debian), exim4 (Ubuntu), exim4-daemon-heavy (Ubuntu), exim4-daemon-light (Ubuntu). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-11-07.