CVE-2018-6789

CVE-2018-6789 is a critical-severity vulnerability in Exim with a CVSS 3.x base score of 9.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2021-11-03). The underlying weakness is classified as CWE-120.

Key facts

• Severity: Critical (CVSS 3.x base score 9.8)
• CVSS v2: 7.5
• EPSS exploit prediction: 82% (100th percentile)
• Actively exploited: Yes — listed in CISA KEV (added 2021-11-03)
• EU (EUVD) id: EUVD-2018-18536
• EU exploitation: Flagged exploited in the ENISA EU Vulnerability Database (since 2021-11-03)
• Weakness: CWE-120
• Affected product: Exim
• Published: 2018-02-08
• Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2018-6789?

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 severe is CVE-2018-6789?

CVE-2018-6789 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2018-6789 being actively exploited?

Yes. CVE-2018-6789 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2018-6789?

CVE-2018-6789 primarily affects Exim. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2018-6789?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

Does CVE-2018-6789 have an EU (EUVD) identifier?

Yes. CVE-2018-6789 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2018-18536. It is also flagged as exploited in the EUVD (since 2021-11-03).

When was CVE-2018-6789 published?

CVE-2018-6789 was published on 2018-02-08 and last updated on 2026-06-17.

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/
• https://www.exploit-db.com/exploits/45671/
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2018-6789

Affected products (7)

• cpe:2.3:a:exim:exim:*:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:8.0:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:esm:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:esm:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:17.10:*:*:*:*:*:*:*

More vulnerabilities in Exim

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• CVE-2023-42116 — Critical (CVSS 9.8): Exim SMTP Challenge Stack-based Buffer Overflow Remote Code Execution Vulnerability. This vulnerability allows remote…
• CVE-2023-42115 — Critical (CVSS 9.8): Exim AUTH Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to…
• CVE-2022-37452 — Critical (CVSS 9.8): Exim before 4.95 has a heap-based buffer overflow for the alias list in host_name_lookup in host.c when…
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Threat intelligence

Threat-intel indicators referencing this CVE:

• 5.101.115.170 (ipv4-addr)
• 74.248.33.65 (ipv4-addr)
• 103.90.233.75 (ipv4-addr)
• 206.214.217.154 (ipv4-addr)
• 178.128.21.57 (ipv4-addr)
• 46.101.119.133 (ipv4-addr)