In April 2024, I discovered a high-severity vulnerability in Visual Studio Code (VS Code <= 1.89.1) that allows attackers to escalate a Cross-Site Scripting (XSS) bug into full Remote Code Execution (RCE)—even in Restricted Mode.

The desktop version of Visual Studio Code runs on Electron. Renderer processes are sandboxed and communicate with the main process through Electron’s IPC mechanism.

An XSS vulnerability in the newly-introduced minimal error rendering mode for Jupyter notebooks enables arbitrary JavaScript code to be executed within the vscode-app WebView for the notebook renderer. The vulnerability can be triggered by opening a crafted .ipynb file if the user has the setting enabled, or by opening a folder containing a crafted settings.json file in VS Code and opening a malicious ipynb file within the folder. This vulnerability can be triggered even when Restricted Mode is enabled (which is the default for workspaces that have not been explicitly trusted by the user).

In this post, we’ll walk through how the bug works and how it bypasses VS Code’s Restricted Mode.

Brief I may have achieved successful exploitation of a SharePoint target during Pwn2Own Vancouver 2023. While the live demonstration lasted only approximately 30 seconds, it is noteworthy that the process of discovering and crafting the exploit chain consumed nearly a year of meticulous effort and research to complete the full exploit chain.
This exploit chain leverages two vulnerabilities to achieve pre-auth remote code execution (RCE) on the SharePoint server:
Authentication Bypass – An unauthenticated attacker can impersonate as any SharePoint user by spoofing valid JSON Web Tokens (JWTs), using the none signing algorithm to subvert signature validation checks when verifying JWT tokens used for OAuth authentication.