CVE-2025-50733 is a cross-site scripting (XSS) vulnerability identified in the NextChat application, specifically within the HTMLPreview component of the artifacts.tsx file. This vulnerability arises because the application renders user-influenced HTML content generated by AI responses inside an iframe that has the 'allow-scripts' sandbox permission enabled, but lacks proper sanitization of the HTML content. Attackers can exploit this by crafting malicious prompts that cause the AI to generate HTML or JavaScript code containing harmful scripts. When a user views this HTML preview, the malicious JavaScript executes in the context of the user's browser session. This can lead to several severe consequences, including exfiltration of sensitive data such as API keys stored in localStorage, unauthorized actions performed on behalf of the user, and theft of session information. The vulnerability does not require prior authentication or user interaction beyond viewing the malicious HTML preview, making it particularly dangerous. Although no CVSS score has been assigned yet, the nature of the vulnerability indicates a significant risk to confidentiality, integrity, and availability of user data and sessions within the NextChat environment.

For European organizations using NextChat, this vulnerability poses a critical risk to data confidentiality and user session integrity. Since the exploit allows execution of arbitrary JavaScript in the user's browser, attackers could steal sensitive corporate API keys, session tokens, and other confidential information stored locally, potentially leading to unauthorized access to internal systems or data breaches. The ability to perform actions on behalf of the user could facilitate further lateral movement within corporate networks or manipulation of AI chat interactions, undermining trust in AI-driven communication tools. Given the increasing adoption of AI chat interfaces in business workflows across Europe, exploitation could disrupt operations, cause reputational damage, and lead to compliance violations under regulations such as GDPR due to unauthorized data exposure. The lack of known exploits in the wild currently reduces immediate risk, but the vulnerability's characteristics suggest it could be weaponized rapidly once publicized.

To mitigate this vulnerability, organizations should implement strict input sanitization and output encoding on all HTML content rendered within the AI chat interface, especially in the HTMLPreview component. The iframe sandbox permissions should be tightened by removing 'allow-scripts' unless absolutely necessary, or by employing Content Security Policy (CSP) headers to restrict script execution and resource loading. Developers should consider disabling HTML rendering of AI-generated content or replacing it with safer alternatives such as plain text or sanitized markdown. Regular security code reviews and penetration testing focused on AI-generated content rendering are recommended. Additionally, organizations should monitor for suspicious prompt inputs and user activity that could indicate exploitation attempts. Prompt patching once a fix is released is critical, as is educating users about the risks of interacting with untrusted AI-generated content. Finally, storing sensitive keys and tokens in more secure storage mechanisms than localStorage, such as HttpOnly cookies or secure vaults, can reduce the impact of client-side script attacks.