CVE-2026-67191 — Xlight FTP Server before 3.9.5 contains a pre-authentication heap buffer overflow…¶

Key facts

CVE-2026-67191 is a Critical (9.8) vulnerability: Xlight FTP Server before 3.9.5 contains a pre-authentication heap buffer overflow…. This entry ships a detection-only PoC and a Docker test lab.


CVE	CVE-2026-67191
Severity	Critical (9.8)
Detection / prevention	—
PoC	poc.py
Source	2026/CVE-2026-67191/

Details¶

English | 한국어

Description¶

Xlight FTP Server before 3.9.5 contains a pre-authentication heap buffer overflow vulnerability that allows remote unauthenticated attackers to write past the end of a heap buffer by sending a malformed SSH client identification string. A logic error in the recv loop's termination condition uses an incorrect OR operator where an AND operator is required, enabling exploitation on any SSH or SFTP connection before authentication occurs.

Vulnerability Details¶

Property	Value
CVE ID	CVE-2026-67191
CVSS Score	9.8

Proof of Concept¶

Download¶

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-67191/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-2026-67191

# 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¶

https://www.vulncheck.com/advisories/xlight-ftp-server-pre-auth-heap-buffer-overflow-via-ssh-parser
https://www.xlightftpd.com/whatsnew.htm

Generated by PoC Generator on 2026-08-02T21:00:27.007646162

Frequently asked questions¶

What is CVE-2026-67191?¶

CVE-2026-67191 is a Critical (9.8) vulnerability: Xlight FTP Server before 3.9.5 contains a pre-authentication heap buffer overflow…. This entry ships a detection-only PoC and a Docker test lab.

How do I detect CVE-2026-67191?¶

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-2026-67191?¶

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

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