Local Privilege Escalation via Directory Junction in CoworkVMService

The CoworkVMService component in Claude Desktop for Windows ran as SYSTEM and did not validate whether the VM bundle directory was a real directory or an NTFS directory junction before creating files within it. A local non-elevated user could replace the user-writable VM bundle directory with a directory junction pointing to an attacker-chosen location, causing the service to create a SYSTEM-owned file in an arbitrary directory. This could be leveraged for local privilege escalation.

Users are advised to update to the latest version of Claude Desktop for Windows.

Thank you to hackerone.com/piquo for reporting this issue.