CVE-2025-27609: Icinga Web 2 XSS Vulnerability

CVE-2025-27609 Overview

CVE-2025-27609 is a cross-site scripting (XSS) vulnerability in Icinga Web 2, an open source monitoring web interface, framework, and command-line interface. The flaw affects versions prior to 2.11.5 and 2.12.3. An attacker can craft a request that, once transmitted to a victim's Icinga Web session, embeds arbitrary JavaScript into the interface. The injected script executes in the victim's browser context and acts on behalf of the authenticated user. The vulnerability is classified under [CWE-79] (Improper Neutralization of Input During Web Page Generation).

Critical Impact
An attacker who convinces an authenticated Icinga Web 2 user to load a crafted request can execute arbitrary JavaScript in the victim's browser and perform actions with that user's privileges.

Affected Products

Icinga Web 2 versions prior to 2.11.5
Icinga Web 2 versions 2.12.0 through 2.12.2
Icinga icinga_web_2 (all deployments on unpatched releases)

Discovery Timeline

2025-03-26 - CVE-2025-27609 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-27609

Vulnerability Analysis

The vulnerability resides in how Icinga Web 2 processes certain user-controllable request parameters that are subsequently rendered in the web interface. Insufficient output encoding allows an attacker to inject JavaScript payloads that execute in the context of an authenticated user's session.

Exploitation requires user interaction. The attacker must deliver a crafted URL or request to a logged-in Icinga Web 2 user, typically through phishing or a malicious link. Once triggered, the injected script runs with the victim's permissions and can issue API calls, alter monitoring configuration, or exfiltrate session data. The attack vector is local and requires the victim to interact with attacker-supplied content, which reduces the risk profile compared to unauthenticated network exploitation.

Root Cause

The root cause is improper neutralization of user-supplied input before it is embedded in HTML responses generated by Icinga Web 2. The application fails to sanitize or contextually escape data that is reflected back to the browser, allowing HTML and JavaScript to be interpreted rather than displayed as literal text.

Attack Vector

An attacker crafts a request containing a JavaScript payload and delivers it to an authenticated Icinga Web 2 user through social engineering. When the user's browser loads the crafted request, the payload is reflected into the response and executed. The script then operates within the victim's authenticated session and can perform any action the user is permitted to perform in Icinga Web 2. See the GitHub Security Advisory GHSA-5cjw-fwjc-8j38 for additional technical context.

Detection Methods for CVE-2025-27609

Indicators of Compromise

Unexpected HTTP requests to Icinga Web 2 endpoints containing HTML tags, <script> fragments, javascript: URIs, or encoded payloads such as %3Cscript%3E in query parameters.
Web server access logs showing referrers from untrusted external domains preceding Icinga Web 2 sessions.
Anomalous API activity performed by legitimate user accounts, particularly configuration changes or credential-related actions initiated shortly after clicking external links.
Content Security Policy violation reports (when CSP is enabled) referencing inline script execution on Icinga Web 2 pages.

Detection Strategies

Deploy a web application firewall (WAF) with signatures for reflected XSS patterns targeting Icinga Web 2 request parameters.
Correlate authentication logs with web request logs to identify sessions that executed sensitive actions immediately after loading externally referred URLs.
Enable Content Security Policy reporting to capture violations indicative of injection attempts.
Monitor for browser-side errors and CSP reports centralized in a SIEM for pattern analysis.

Monitoring Recommendations

Log and inspect all query strings and POST bodies to Icinga Web 2 for HTML metacharacters and known XSS keywords.
Alert on any Icinga Web 2 access originating from external HTTP referrers, since the interface is typically internal.
Track configuration and command dispatch events by user, flagging deviations from that user's baseline behavior.

How to Mitigate CVE-2025-27609

Immediate Actions Required

Upgrade Icinga Web 2 to version 2.11.5 or 2.12.3 (or later) immediately.
Inventory all Icinga Web 2 instances and prioritize internet-exposed or shared deployments for patching first.
Educate operators to avoid clicking untrusted links while authenticated to monitoring interfaces.
Force session invalidation after upgrade to terminate any potentially hijacked sessions.

Patch Information

Icinga has released fixed builds. Upgrade to Icinga Web 2.11.5 or Icinga Web 2.12.3. Both releases contain the sanitization fix that eliminates the reflected script injection vector. Review the vendor security advisory GHSA-5cjw-fwjc-8j38 for release-specific notes.

Workarounds

Operators running Icinga Web 2.12.2 can enable a Content Security Policy in application settings as a temporary mitigation until upgrade.
Ensure users access Icinga Web 2 only through modern browsers with working CORS enforcement, which sufficiently guards against the vulnerability.
Restrict Icinga Web 2 access to trusted network segments and require VPN authentication to reduce exposure to phishing-delivered payloads.
Enforce short session lifetimes and require re-authentication for sensitive configuration changes.

bash

# Configuration example: enable Content Security Policy in Icinga Web 2 config.ini
# File: /etc/icingaweb2/config.ini
[security]
content_security_policy = 1