CVE-2026-2736 in OpenCms
Summary
by MITRE • 02/19/2026
Reflected Cross-site Scripting (XSS) in Alkacon's OpenCms v18.0, which allows an attacker to execute JavaScript code in the victim's browser by sending the victim a malicious URL containing the ‘q’ parameter in ‘/search/index.html’. This vulnerability can be exploited to steal sensitive user information such as session cookies, or to perform actions while impersonating the user.
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Analysis
by VulDB Data Team • 02/19/2026
This reflected cross-site scripting vulnerability exists in Alkacon's OpenCms version 18.0 within the search functionality at /search/index.html. The flaw occurs when the application fails to properly sanitize or escape user input passed through the 'q' parameter, allowing malicious scripts to be injected and executed in the context of the victim's browser. The vulnerability represents a classic reflected XSS attack vector where an attacker crafts a malicious URL containing crafted JavaScript code within the query parameter and sends it to unsuspecting users. When victims click the malicious link, their browsers execute the injected script in the context of the vulnerable OpenCms application, potentially compromising user sessions and sensitive data.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding practices within the search module. The application processes the 'q' parameter without adequate sanitization measures, directly incorporating user-supplied content into dynamically generated HTML responses. This failure to properly escape or filter user input creates an environment where attacker-controlled scripts can be executed with the privileges of the authenticated user. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and demonstrates characteristics consistent with ATT&CK technique T1566.001 for initial access through spearphishing attachments or links. The reflected nature of the vulnerability means that the malicious payload is reflected back to the user through the application's response rather than being stored on the server, making it particularly challenging to detect and prevent through traditional security measures.
The operational impact of this vulnerability extends beyond simple script execution to encompass serious security implications for user data and application integrity. Attackers can leverage this vulnerability to steal session cookies, effectively hijacking user sessions and gaining unauthorized access to protected resources. Additionally, the compromised user context allows for privilege escalation attacks where malicious actions can be performed on behalf of the victim, including data manipulation, unauthorized file access, or even complete account takeovers. The vulnerability also enables more sophisticated attacks such as credential theft, data exfiltration, or the deployment of additional malware through the victim's browser. Organizations running OpenCms v18.0 are particularly at risk since the vulnerability affects core search functionality that is likely to be frequently accessed by legitimate users.
Mitigation strategies for this reflected XSS vulnerability should include immediate implementation of proper input validation and output encoding mechanisms. The application must sanitize all user input through comprehensive validation routines that reject or escape potentially malicious content before processing. Specifically, the 'q' parameter should be properly encoded when rendered in HTML contexts to prevent script execution. Organizations should implement Content Security Policy (CSP) headers to limit script execution sources and prevent unauthorized code injection. Additionally, regular security updates and patches should be applied immediately upon release, as this vulnerability represents a known flaw that has likely been addressed in subsequent versions of OpenCms. Input filtering should be implemented at multiple levels including application layer validation, web application firewall rules, and proper HTML escaping for dynamic content rendering. The security team should also conduct comprehensive code reviews to identify similar vulnerabilities in other parameters and application modules, ensuring that all user-supplied inputs are properly validated and sanitized according to established security best practices.