3CX before 18 Update 2 Security Hotfix build 18.0.2.315 on Windows allows unauthenticated remote attackers to read certain files via /Electron/download directory traversal. Files may have credentials, full backups, call recordings, and chat logs.
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.