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The vulnerability CVE-2025-66481 in DeepChat (versions 0.5.1 and below) stems from insufficient sanitization of user-supplied Mermaid diagram content. The application’s security patch for the `MermaidArtifact.vue` component was designed to strip dangerous HTML attributes using a regex filter. However, this filter can be bypassed by crafting Mermaid markup that uses unquoted HTML attributes combined with HTML entity encoding (e.g., `"` for a quotation mark). This allows an attacker to inject arbitrary JavaScript payloads into the rendered page context.
The impact escalates to Remote Code Execution (RCE) because DeepChat, as an Electron-based application, exposes the `electron.ipcRenderer` interface to the web page. A successful Cross-Site Scripting (XSS) attack can leverage this interface to send arbitrary IPC messages from the renderer process to the main Node.js process. This bypasses Electron’s context isolation and sandboxing, enabling the execution of system commands on the victim’s machine. The initial regex filter fails to block this attack chain because the encoded payload is decoded after filtering occurs.
Platform: DeepChat
Version: <= 0.5.1
Vulnerability: XSS to RCE
Severity: Critical
date: 2025-12-08
Prediction: Patch by 2026-01-20
What Undercode Say:
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Check local DeepChat version
find /path/to/deepchat -name "package.json" -exec grep '"version"' {} \;
Example malicious Mermaid snippet for testing (encoded)
echo 'graph TD;A["<img src=x onerror=alert`1`>"];'
Isolate and audit the vulnerable component
grep -r "MermaidArtifact" /path/to/deepchat/src --include=".vue"
// Example exploit payload bypassing regex via encoding
const mermaidPayload = <code>graph LR;A["<img src=x onerror="window.electron.ipcRenderer.send('system-cmd', 'calc.exe')">"]</code>;
How Exploit:
- Attacker crafts a Mermaid diagram with an encoded JavaScript payload targeting the `electron.ipcRenderer` API.
- This payload is embedded in a chat message or saved artifact within DeepChat.
- When a victim views the tainted content, the encoded payload is decoded by the browser after passing the flawed sanitizer.
- The injected script executes in the victim’s session, using the IPC interface to run system commands, achieving full RCE.
Protection from this CVE:
Immediately disable Mermaid diagram rendering in the chat.
Implement strict Content Security Policy (CSP) headers to block inline scripts.
Apply context-aware HTML entity encoding before running input through the regex sanitizer.
Review and harden all `ipcRenderer` exposure in the Electron main process.
Impact:
Full compromise of the client application on a user’s desktop.
Remote execution of arbitrary commands on the victim’s operating system.
Potential theft of local files, credentials, and system access.
Complete bypass of Electron sandbox security controls.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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