CVE-2026-78209 — exceljs-hardened versions before 5.0.0 fail to neutralize leading equals, plus, minus, or…¶
Key facts
CVE-2026-78209 is a High (8.2) vulnerability: exceljs-hardened versions before 5.0.0 fail to neutralize leading equals, plus, minus, or…. This entry ships a detection-only PoC and a Docker test lab.
| CVE | CVE-2026-78209 |
| Severity | High (8.2) |
| Detection / prevention | — |
| PoC | poc.py |
| Source | 2026/CVE-2026-78209/ |
Details¶
English | 한국어
Description¶
exceljs-hardened versions before 5.0.0 fail to neutralize leading equals, plus, minus, or at signs in cell values written to CSV output. Attackers who can influence exported cell values can inject formulas that execute when the CSV file is opened in a spreadsheet application, potentially exfiltrating data or performing other malicious actions.
Vulnerability Details¶
| Property | Value |
|---|---|
| CVE ID | CVE-2026-78209 |
| CVSS Score | 8.2 |
Proof of Concept¶
Download¶
# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-78209/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-2026-78209
# 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://github.com/exceljs/exceljs
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/csv/csv.js#L109-L182
- https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-9wxc-4rhw-hfrw
- https://www.vulncheck.com/advisories/exceljs-through-csv-formula-injection-via-unescaped-cell-values
Generated by PoC Generator on 2026-08-24T13:05:01.229032633
Frequently asked questions¶
What is CVE-2026-78209?¶
CVE-2026-78209 is a High (8.2) vulnerability: exceljs-hardened versions before 5.0.0 fail to neutralize leading equals, plus, minus, or…. This entry ships a detection-only PoC and a Docker test lab.
How do I detect CVE-2026-78209?¶
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-2026-78209?¶
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.