Cursor urged developers who installed malicious Claude Code packages from Cursor's marketplace to clean affected machines. Cursor also advised using a trusted system to rotate credentials and sessions accessible from affected hosts. Cursor warned that persistent components may remain active after developers uninstall the extension.
Cursor identified the affected packages as Anthropic.claude-code versions 2.1.312 and 2.1.313 for macOS and Windows. Cursor's security notice says the packages were available on Oct. 29, 2026, from about 2:27 a.m. to 1:35 p.m. PT. Cursor said Anthropic was not responsible for developing the malicious versions. Cursor reported no evidence of effects on other versions or the official distribution.
Cursor clarified the affected versions and indicators on Oct. 30. Security researcher Phorion expanded the malware analysis on Oct. 31 to cover both versions after initially identifying only 2.1.313.
Phorion said the payload attempts to install an attacker-controlled SSH key, activate SSH remote login and create a reverse tunnel. Phorion said the planted key could allow an attacker to connect through the tunnel if SSH is running. Phorion identified a macOS LaunchAgent as a persistence mechanism. Phorion said the Windows payload attempts to create a scheduled task and uses the Startup folder as a fallback.
Phorion said Node executes the injected code while loading the extension module, before the extension's normal activation callback. Phorion said execution requires no additional interaction with the extension at that stage. Phorion found that a permission-check bug prevents the macOS code from enabling Remote Login under a standard user account. Phorion said the planted key could still provide access through an operational tunnel if SSH was already enabled or became enabled later.
Cursor said cooperation with the hosting provider resulted in the attacker server being taken offline. Cursor also removed the malicious packages, rotated Cursor's keys, and rebuilt and reopened the marketplace. Those measures do not eliminate components previously installed on affected machines.
Phorion said the initial beacon transmitted host information and up to 40 matching environment-variable names, but not the variables' secret values. Cursor warned that the limited initial collection does not exclude subsequent credential access through the backdoor. For crypto developers, Cursor's guidance would cover development or financial-service credentials accessible to the affected local user account, if present. Neither advisory establishes cryptocurrency theft or targeting specific to cryptocurrency.
Cursor recommended reviewing endpoint records, network records and extension-installation records. Cursor advised isolating hosts with signs that the payload executed or the backdoor was installed. Cursor recommended removing unauthorized SSH keys, persistence mechanisms and active tunnels. Cursor's notice includes remediation scripts for each platform and recommends evaluating whether affected hosts need rebuilding.
Cursor Warns of Malicious Claude Code Packages in Marketplace
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Summary
Cursor has issued a security alert about malicious Claude code packages in its marketplace, as the fear and greed index in the crypto space remains volatile. The affected versions, 2.1.312 and 2.1.313 for macOS and Windows, were available for 11 hours from October 29, 2026. The malware attempts to install an attacker-controlled SSH key and create a reverse tunnel. Cursor has removed the packages and reopened the marketplace, but warned users to clean machines and rotate credentials. With altcoins to watch under increased scrutiny, security remains a top priority for developers and traders.
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