Malicious Version of Claude Code Extension for VS Code Contained Hidden Remote Access

Developers using Claude AI through Visual Studio Code (VS Code) may have encountered a serious threat: a malicious version of Claude Code was discovered in the Open VSX extension registry. According to a cybersecurity report by OpenSourceMalware dated October 30, version 2.1.313 contained a hidden remote access mechanism that could give attackers access to infected computers. The extension looked and functioned like a legitimate Claude Code tool, making detection particularly difficult.

When the extension was downloaded, additional malicious code was executed. Upon activation, it attempted to establish a remote connection with a server controlled by the attacker, potentially opening access to the victim's computer. The mechanism was designed to remain active even after a reboot: simply closing VS Code or stopping work with Claude might not eliminate the threat.

For blockchain project developers, the risk is higher: their computers may store private keys, wallet data, exchange API keys, and access to cryptocurrency infrastructure. With successful remote access, this data could be used to compromise wallets or projects. However, researchers have not reported confirmed cryptocurrency theft and did not identify specific blockchain functionality in the malicious code.

Researchers confirmed the malicious code in the analyzed version of Open VSX but did not determine how it was introduced. The findings do not prove that the official Anthropic release in the VS Code Marketplace or broader distribution systems were compromised. Those who installed version 2.1.313 via Open VSX are advised to consider their systems potentially compromised and conduct an immediate check. Removing the extension may not be sufficient: the mechanism was designed to persist independently.