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CVE-2018-6789 — An issue was discovered in the base64d function in the SMTP listener in Exim before…

Key facts

CVE-2018-6789 is a Critical (9.8) vulnerability: An issue was discovered in the base64d function in the SMTP listener in Exim before…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2021-11-03), confirming active exploitation in the wild, and is linked to known ransomware campaigns.

Actively exploited — on the CISA KEV catalog

CVE-2018-6789 is listed on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2021-11-03), confirming exploitation in the wild. It is linked to known ransomware campaigns. Federal remediation deadline: 2022-05-03. Prioritise patching and deploy the detection and prevention rules below.
CVE CVE-2018-6789
Severity Critical (9.8)
CISA KEV Actively exploited (added 2021-11-03) · ransomware
Detection / prevention —
PoC poc.py
Source 2018/CVE-2018-6789/

Details

English | 한국어

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.

Vulnerability Details

Property Value
CVE ID CVE-2018-6789
CVSS Score 9.8

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2018/CVE-2018-6789/poc.py

Usage

# Run PoC against target
python3 poc.py --target <TARGET_URL>

# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>

⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.

Test Lab

This repository includes a Docker-based test environment with both vulnerable and patched applications.

Quick Start

# Clone and navigate to CVE directory
cd CVE-2018-6789

# Start both applications
docker-compose up -d

# Run tests
./run-tests.sh    # Linux/Mac
./run-tests.ps1   # Windows PowerShell

Application Endpoints

Application URL Status
Vulnerable App http://localhost:8080 Shows vulnerability
Patched App http://localhost:8081 Demonstrates fix

Directory Structure

├── README.md           # English documentation
├── README_KO.md        # Korean documentation
├── poc.py              # PoC detection script
├── docker-compose.yml  # Container orchestration
├── run-tests.sh        # Linux/Mac test runner
├── run-tests.ps1       # Windows test runner
├── vulnerable-app/     # Vulnerable version
│   ├── app.py
│   ├── Dockerfile
│   └── requirements.txt
└── patched-app/        # Fixed version
    ├── app.py
    ├── Dockerfile
    └── requirements.txt

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/
  • 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

Generated by PoC Generator on 2026-07-03T09:12:20.108588856

Frequently asked questions

What is CVE-2018-6789?

CVE-2018-6789 is a Critical (9.8) vulnerability: An issue was discovered in the base64d function in the SMTP listener in Exim before…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2021-11-03), confirming active exploitation in the wild, and is linked to known ransomware campaigns.

How do I detect CVE-2018-6789?

Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.

How do I block or mitigate CVE-2018-6789?

Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.

Is CVE-2018-6789 actively exploited?

Yes. CVE-2018-6789 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2021-11-03, which means it has been exploited in the wild. CISA also links it to known ransomware campaigns. CISA set a federal remediation deadline of 2022-05-03. Prioritise patching and deploy the detection and prevention rules above.

For authorized security testing and research only. See the full source and NVD record.