CVE-2026-76842 — The Mercado Pago Node.js SDK interpolates caller-supplied identifiers into API request…¶

Key facts

CVE-2026-76842 is a High (8.2) vulnerability: The Mercado Pago Node.js SDK interpolates caller-supplied identifiers into API request…. This entry ships a detection-only PoC and a Docker test lab.


CVE	CVE-2026-76842
Severity	High (8.2)
Detection / prevention	—
PoC	poc.py
Source	2026/CVE-2026-76842/

Details¶

English | 한국어

Description¶

The Mercado Pago Node.js SDK interpolates caller-supplied identifiers into API request paths without percent-encoding them, so characters that are structural in a URL survive into the outgoing request. The payment (get, capture, cancel), paymentRefund (create, total, list, get), advancedPayment (get, capture, cancel, update, updateReleaseDate) and disbursementRefund (create, createAll, listAll) clients build their path as a template literal, for example RestClient.fetch(/v1/payments/${id}, ...) in src/clients/payment/get/index.ts. A dot-dot or slash sequence in the identifier is normalised by the WHATWG URL parser and redirects the request to a different endpoint, and a question mark appends attacker-chosen query parameters, in both cases carrying the merchant's own access token. An application that forwards an identifier influenced by an untrusted party into one of these methods without an ownership check therefore allows that party to reach other resources within the merchant's token scope. The repository already contains the intended helper, encodePathParam in src/utils/path.ts, which pull request 451 applied to roughly 29 other clients while leaving these unchanged.

Vulnerability Details¶

Property	Value
CVE ID	CVE-2026-76842
Type	RCE
CVSS Score	8.2

Proof of Concept¶

Download¶

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-76842/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-2026-76842

# 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/mercadopago/sdk-nodejs
https://github.com/mercadopago/sdk-nodejs/blob/3.4.0/src/clients/payment/get/index.ts
https://github.com/mercadopago/sdk-nodejs/pull/451
https://www.vulncheck.com/advisories/mercado-pago-node-js-sdk-through-path-injection-via-unencoded-identifiers-in-payment-clients

Generated by PoC Generator on 2026-08-25T00:45:52.591057144

Frequently asked questions¶

What is CVE-2026-76842?¶

CVE-2026-76842 is a High (8.2) vulnerability: The Mercado Pago Node.js SDK interpolates caller-supplied identifiers into API request…. This entry ships a detection-only PoC and a Docker test lab.

How do I detect CVE-2026-76842?¶

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-2026-76842?¶

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.