CVE-2026-89145 in Flextype
Summary
by MITRE • 09/11/2026
Flextype CMS versions 0.9.9 through 1.0.0-alpha.3 fail to HTML-escape plugin directory names in the dependency error page rendered by getValidPluginsDependencies(). Attackers with write access to the plugins directory can create a plugin with HTML characters in its name to execute arbitrary scripts in users' browsers when dependency validation fails.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 09/11/2026
The vulnerability identified in Flextype CMS versions 0.9.9 through 1.0.0-alpha.3 represents a classic Stored Cross-Site Scripting flaw rooted in insufficient input sanitization during the rendering of system error messages. Specifically, the function getValidPluginsDependencies() is responsible for validating plugin dependencies and generating an HTML response when validation fails. In this process, the application incorporates the directory name of the offending plugin directly into the output without applying proper HTML entity encoding or escaping mechanisms. This oversight allows any special characters present in the plugin's file system path to be interpreted as executable code by the victim's web browser rather than being displayed as literal text.
The operational impact of this vulnerability is significant for environments where multiple users have write access to the plugins directory, such as collaborative development setups or poorly configured shared hosting environments. An attacker with these specific privileges can create a malicious plugin file within a directory whose name contains HTML tags and JavaScript payloads. When an administrator or another user attempts to view the dependency status of this plugin, the system triggers the error page containing the unescaped payload. Consequently, arbitrary scripts execute in the context of the victim's session, potentially leading to account takeover through cookie theft, redirection to phishing sites, or defacement of the administrative interface. This aligns with CWE-79, which classifies improper neutralization of input during web page generation as a Cross-site Scripting vulnerability.
From an attacker perspective, this flaw facilitates persistent malicious code execution without requiring direct injection into content fields, leveraging instead the system's own error handling logic to deliver the payload. The attack vector is categorized under ATT&CK technique T1059, specifically Command and Scripting Interpretation via JavaScript in a web browser context. Because the script executes within the domain of the CMS administrative interface, it inherits all associated privileges, including access to sensitive configuration files, database credentials stored in plaintext or encrypted formats, and the ability to modify site content. This persistence mechanism ensures that every subsequent visit by an authorized user results in further exploitation until the malicious plugin is removed.
Mitigation strategies must focus on both immediate remediation and long-term defensive coding practices. Administrators should immediately update Flextype CMS to a version where this issue has been patched, ensuring that all input data rendered in HTML contexts undergoes rigorous encoding. Developers implementing similar systems must adopt a whitelist approach for allowed characters in directory names or enforce strict output encoding using established libraries such as OWASP Java Encoder or equivalent frameworks for other languages. Additionally, implementing Content Security Policy headers can provide an additional layer of defense by restricting the sources from which scripts are loaded and executed, thereby mitigating the impact even if input validation fails. Regular security audits focusing on error handling routines are essential to prevent similar oversights in future development cycles.