Malicious Claude Code Extension Targets 5,000 Users on Cursor Market

The developers of the AI-integrated code editor Cursor have issued an urgent security alert regarding a fraudulent version of the Claude Code extension. A malicious actor successfully uploaded a tampered version of the tool to the Cursor extension marketplace, potentially compromising the workstations of up to 5,000 users. This incident highlights the growing security risks within the AI-assisted development ecosystem, where attackers leverage the popularity of Anthropic’s models to distribute malware.

Mechanism of the Extension Attack

The security breach involved version 2.1.313 of the Claude Code extension, which was falsely presented as an official product. Upon installation, the malicious software initiated unauthorized processes designed to extract sensitive data from the developer's environment. According to Cursor’s security announcement, the extension's primary functions included:

• Collecting user host information to identify potential high-value targets.
• Attempting to implant an SSH backdoor, allowing for persistent remote access to the infected system.
• Circumventing standard security protocols typically associated with official VS Code compatible extensions.

Anthropic, the creator of the Claude AI model, has confirmed it did not develop or authorize the 2.1.313 version found on the marketplace.

Remediation and Safety Recommendations

Cursor officials acted quickly to remove the compromised software from their platform once the threat was identified on October 30, 2026. To mitigate the risk of data theft or unauthorized system control, the team has released a clean update. Users are strongly advised to verify their current installations and ensure they have transitioned to version 2.1.314, which contains the necessary security patches.

Cursor has removed the extension and recommends users update the Claude Code extension to version 2.1.314 to ensure system integrity.

As AI tools become integral to blockchain development and smart contract coding, such supply chain attacks represent a significant threat to the security of digital assets and private keys stored on developer machines. The incident serves as a reminder for the cryptocurrency community and software engineers to exercise caution when installing third-party plugins, even within trusted marketplaces. Users who suspect they were infected should audit their SSH keys and rotate sensitive credentials immediately.