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Introduction

In cybersecurity, simple mistakes often lead to critical vulnerabilities. One such case is CVE-2023-35759 — a Cross-Site Scripting (XSS) flaw in popular network monitoring software, WhatsUp Gold, discovered in versions before 23... This post will break down this vulnerability, show you a proof-of-concept exploit, and explain how such issues can creep into enterprise tools. All content is exclusive, explained in plain English for easy understanding.

What is WhatsUp Gold?

WhatsUp Gold is an SNMP (Simple Network Management Protocol) and network monitoring application used by organizations to keep track of their IT assets, devices, and services. It provides a web-based interface where admins can view alerts, reports, and device data.

Impact: Remote code execution in user's browser (under the victim's privileges)

Summary:
The vulnerability exists because WhatsUp Gold's SNMP monitoring endpoints failed to sanitize user-supplied input. An attacker could inject malicious code, typically JavaScript, which is then executed by the victim's browser if they visit a specially crafted page.

How the Bug Happens

WhatsUp Gold parses SNMP messages or parameters provided via HTTP requests (think: GET or POST requests). The vulnerable endpoint accepted raw input parameters—such as device names, status, SNMP strings, etc.—and reflected them back into the admin interface.

If that input wasn’t sanitized or escaped, and someone included HTML or JavaScript code, it could be executed in any administrator's browser who viewed the affected page.

Input sent via SNMP or HTTP API:

- Via SNMP trap or direct HTTP endpoint (using tools like curl, Burp Suite, or a custom exploit script).

Victim visits WhatsUp Gold interface:

The web app displays the device name on the dashboard without filtering, immediately executing JavaScript payload in the victim's browser.

Proof-of-Concept Exploit

Here’s a simple curl example to add a malicious device via the vulnerable endpoint (adapt as needed):

curl -X POST \
  'http://whatsupgold.local/api/devices/add'; \
  -H 'Content-Type: application/json' \
  -d '{"deviceName": "<img src=x onerror=alert(document.domain)>", "ip": "1.2.3.4"}'

Any admin who views the device list will trigger the injected alert.

Vulnerable code sketch (hypothetical example)

@app.route("/devices/add", methods=["POST"])
def add_device():
    # Device name comes directly from user input.
    device_name = request.json["deviceName"]
    # Saved to database and later rendered like:
    return render_template("device.html", device_name=device_name)

FIX: Sanitize Input

Proper fix: Escape HTML special characters before rendering any user-controlled string.

Example using Python's Flask

from markupsafe import escape

@app.route("/devices/add", methods=["POST"])
def add_device():
    device_name = escape(request.json["deviceName"])
    return render_template("device.html", device_name=device_name)

Or, use built-in escaping in your template engine (e.g., Jinja2 auto-escaping).

References

- NIST NVD CVE-2023-35759
- Progress WhatsUp Gold Security Updates
- OWASP XSS Prevention Cheat Sheet

Final Notes

If you use WhatsUp Gold before 23.., update immediately to avoid this attack. XSS flaws are easy to underestimate but can utterly compromise your network—since network admins have high privileges, a single successful attack could mean full access.

Pro tip: Always sanitize user input, no matter where it comes from! Even internal protocols like SNMP can become the source of security nightmares.

Timeline

Published on: 06/23/2023 20:15:00 UTC
Last modified on: 07/03/2023 16:24:00 UTC