DeepChat's Incomplete XSS Fix Allows RCE through Mermaid Content

The vulnerability stems from improper sanitization of Mermaid content within DeepChat. Attackers can exploit this by injecting malicious Mermaid code containing unquoted HTML attributes combined with HTML entity encoding. This bypasses the intended regex filter, allowing for the execution of arbitrary JavaScript code within the context of the user's browser. The use of electron.ipcRenderer amplifies the impact, potentially enabling attackers to execute code directly on the victim's machine, rather than just within the browser environment. This could lead to data theft, account compromise, or even complete system takeover, depending on the privileges of the user running DeepChat.

Organizations and individuals deploying DeepChat, particularly those using it in environments where user-supplied content is processed, are at risk. Shared hosting environments where multiple users share the same DeepChat instance are especially vulnerable, as an attacker could potentially compromise the entire environment through a single user's account.

• javascript / web: Inspect DeepChat application code for instances of electron.ipcRenderer calls with unsanitized user input. • javascript / web: Monitor network traffic for requests containing suspicious Mermaid code patterns, particularly those with unquoted HTML attributes and HTML entity encoding. • javascript / web: Use browser developer tools to identify and analyze any unexpected JavaScript execution within the DeepChat application. • javascript / web: Review DeepChat logs for any errors or warnings related to Mermaid parsing or rendering.

1. 2025-12-09Disclosure

   disclosure

1. Reserviert2025-12-02
2. Veröffentlicht2025-12-09
3. EPSS aktualisiert2026-03-23

The primary mitigation is to immediately upgrade DeepChat to version 0.5.2 or later, which includes the necessary fix. If upgrading is not immediately feasible, consider implementing a Web Application Firewall (WAF) rule to block requests containing suspicious Mermaid code patterns, specifically those utilizing unquoted HTML attributes and HTML entity encoding. Carefully review and restrict the permissions granted to the electron.ipcRenderer interface to limit the potential damage from successful exploitation. Monitor DeepChat logs for any unusual activity or attempts to inject malicious code.