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. The vulnerability arises because the application renders user-influenced HTML content generated by AI responses inside an iframe that is sandboxed with the 'allow-scripts' permission but lacks proper sanitization of the HTML content. This setup allows attackers to craft malicious prompts that cause the AI to generate harmful HTML and JavaScript code. When a user views this HTML preview in the chat interface, the malicious JavaScript executes within the user's browser context. This execution can lead to the exfiltration of sensitive data such as API keys stored in localStorage, session hijacking, and unauthorized actions performed on behalf of the user. The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), indicating a classic reflected/stored XSS flaw. The CVSS v3.1 base score is 6.1 (medium severity), with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), user interaction required (UI:R), scope changed (S:C), and low impact on confidentiality and integrity (C:L, I:L) but no impact on availability (A:N). No patches or known exploits are currently reported, but the vulnerability's presence in an AI chat interface that renders dynamic HTML content makes it a significant risk if exploited. The core issue is the unsafe rendering of AI-generated HTML without sufficient sanitization, combined with the iframe sandbox configuration that permits script execution, enabling attackers to bypass typical browser security boundaries.

For European organizations using NextChat or similar AI chat interfaces that render HTML content, this vulnerability poses a risk of sensitive data leakage, including API keys and session tokens, which could lead to unauthorized access to internal systems or cloud services. The ability to execute arbitrary JavaScript in users' browsers can facilitate further attacks such as credential theft, session hijacking, or lateral movement within corporate networks. Since the vulnerability requires user interaction (viewing the malicious HTML preview), phishing or social engineering campaigns could be used to trigger exploitation. The impact is particularly critical for organizations relying on NextChat for internal communications or development workflows where API keys and session data are stored in localStorage. Confidentiality and integrity of sensitive information are at risk, potentially leading to data breaches, compliance violations (e.g., GDPR), and reputational damage. The medium severity score reflects the need for prompt mitigation but also indicates that exploitation is not trivial without user interaction.

To mitigate this vulnerability, organizations should implement strict input sanitization and output encoding on all AI-generated HTML content before rendering it in the chat interface. Employ robust HTML sanitization libraries that remove or neutralize potentially dangerous tags and attributes, especially script elements and event handlers. Modify the iframe sandbox permissions to remove 'allow-scripts' unless absolutely necessary, or consider rendering HTML previews in a more restrictive environment that disallows script execution entirely. Implement Content Security Policy (CSP) headers to restrict the execution of inline scripts and loading of external resources within the iframe context. Educate users about the risks of interacting with untrusted AI-generated content and encourage caution when viewing HTML previews. Monitor logs for unusual activity related to the HTMLPreview component and consider deploying runtime application self-protection (RASP) solutions to detect and block XSS attempts. Finally, coordinate with NextChat developers or vendors to obtain patches or updates that address this vulnerability and apply them promptly once available.