CVE-2023-42343: Alkacon OpenCMS XSS Vulnerability

CVE-2023-42343 Overview

CVE-2023-42343 is a reflected Cross-Site Scripting (XSS) vulnerability in Alkacon OpenCms versions prior to 10.5.1. The flaw resides in the cmis-online/type endpoint, which fails to properly sanitize user-supplied input before reflecting it in HTTP responses. Attackers can craft malicious URLs that execute arbitrary JavaScript in the context of a victim's browser session. Successful exploitation requires user interaction, such as clicking a crafted link. The vulnerability is categorized under [CWE-79] (Improper Neutralization of Input During Web Page Generation).

Critical Impact
Attackers can execute arbitrary JavaScript in authenticated user sessions, enabling session token theft, credential harvesting, and unauthorized actions within the OpenCms application.

Affected Products

Alkacon OpenCms versions prior to 10.5.1
The cmis-online/type endpoint is the vulnerable component
Web applications and content management deployments built on affected OpenCms versions

Discovery Timeline

2026-05-08 - CVE-2023-42343 published to NVD
2026-05-08 - Last updated in NVD database

Technical Details for CVE-2023-42343

Vulnerability Analysis

The vulnerability exists in the cmis-online/type URL path handler within Alkacon OpenCms. The application takes input from the request URI and reflects it into the generated HTTP response without applying proper output encoding or input sanitization. An attacker who controls the URL path or its parameters can inject HTML and JavaScript that the victim's browser will parse and execute.

Because the injected script executes within the origin of the OpenCms application, it inherits access to cookies, session storage, and the Document Object Model (DOM) of authenticated users. The scope change indicated by the CVSS vector reflects that the attack can affect resources beyond the vulnerable component itself.

Root Cause

The root cause is missing or insufficient output encoding when application data flows from the request URI into HTML response content. The cmis-online/type handler does not neutralize special characters such as <, >, ", and ' before embedding them into the response body. This classic [CWE-79] pattern allows browser-interpreted markup to be injected through attacker-controlled request data.

Attack Vector

Exploitation occurs over the network and requires user interaction. An attacker delivers a crafted link to a victim using phishing email, instant messaging, or a malicious referrer. When the victim follows the link to a vulnerable OpenCms instance, the embedded payload renders in their browser. The Watchtowr Labs research on OpenCms documents related injection patterns in the platform. See the Watchtowr Blog: XXE in OpenCMS for related technical context on OpenCms input handling weaknesses.

No proof-of-concept code is published in the verified references for this specific CVE. The vulnerability manifests when reflected URL path segments containing script payloads are rendered in the HTTP response without HTML entity encoding.

Detection Methods for CVE-2023-42343

Indicators of Compromise

HTTP requests to /cmis-online/type paths containing URL-encoded angle brackets, script tags, or JavaScript event handlers such as onerror= and onload=
Web server access logs showing unusual long URL paths with reflected payload characters under the cmis-online route
Outbound browser requests from internal users to attacker-controlled domains shortly after visiting OpenCms URLs

Detection Strategies

Inspect web application firewall (WAF) and reverse proxy logs for XSS signatures targeting OpenCms endpoints
Correlate user-agent activity with referrer headers pointing to external sources for traffic hitting cmis-online/type
Deploy Content Security Policy (CSP) violation reporting to identify inline script execution attempts

Monitoring Recommendations

Forward OpenCms access logs and WAF telemetry into a centralized analytics platform for query and correlation
Alert on session anomalies such as cookie reuse from new IP addresses following user clicks on external links
Monitor for credential reset spikes, session token theft indicators, and unauthorized administrative actions in OpenCms

How to Mitigate CVE-2023-42343

Immediate Actions Required

Upgrade Alkacon OpenCms to version 10.5.1 or later, which addresses the input handling flaw in cmis-online/type
Audit access logs for prior requests matching XSS patterns against the affected endpoint
Rotate session tokens and force re-authentication for users who may have visited crafted links

Patch Information

Upgrade to Alkacon OpenCms version 10.5.1 or later. Review the vendor release notes for the full set of security fixes included in this and subsequent releases before deploying.

Workarounds

Deploy a WAF rule that blocks or sanitizes requests to /cmis-online/type containing HTML or JavaScript metacharacters
Enforce a strict Content Security Policy that disallows inline scripts and restricts script sources to trusted origins
Restrict network access to OpenCms administrative interfaces using VPN or IP allow-listing until patching is complete

bash

# Example WAF/Nginx rule to block reflected XSS payloads on the vulnerable path
location ~* /cmis-online/type {
    if ($args ~* "(<|%3C)script|onerror=|onload=|javascript:") {
        return 403;
    }
    if ($request_uri ~* "(<|%3C)script|onerror=|onload=") {
        return 403;
    }
}