GHSA-2m8m-jhrm-w6j2: rclone: PowerShell Smart-Quote Filename Injection Enables SFTP Server-Side Command Execution

1. Summary rclone interpolates remote SFTP paths into PowerShell hash commands. Its quoting helper escapes only ASCII apostrophe, although PowerShell accepts four Unicode smart quotes as single-quote delimiters. An attacker-controlled filename can therefore terminate the intended path literal and append PowerShell statements executed as the victim's SSH account. 2. Affected Assets & Attack Surface - Audited commit: a0c09f1381ae93e2a9a33c529d170186c61ad058 - Backend: backend/sftp - Relevant code: - backend/sftp/sftp.go:1802-1812 — PowerShell hash commands - backend/sftp/sftp.go:1663-1699 — Fs.run - backend/sftp/sftp.go:1988-2067 — Object.Hash - backend/sftp/sftp.go:2071-2090 — quoteOrEscapeShellPath - Exposed input: remote filename controlled by an SFTP collaborator, upstream storage source, or other party able to create or rename files. - Required execution context: PowerShell as the SSH command shell, SSH exec enabled, and server-side hashing invoked. 3. Technical Root Cause Analysis For PowerShell, quoteOrEscapeShellPath wraps a path in ASCII apostrophes and doubles only U+0027: return "'" + strings.ReplaceAll(shellPath, "'", "''") + "'", nil Windows PowerShell also treats U+2018, U+2019, U+201A, and U+201B as single-quote delimiters. Those characters pass through the rclone encoder and can close the quoted path. The completed string is sent as shell source through an SSH exec request. The security boundary fails because shell syntax is constructed by string concatenation rather than passing data through a non-code channel. 4. Proof-of-Concept & Evidence - Each of the four Unicode smart quotes was passed through the production quoting function and used to terminate the path literal. - A harmless injected Set-Content statement created a marker file. - The stronger test invoked the exact production Object.Hash path and MD5 PowerShell command against a fake SSH session backed by local PowerShell. - A valid prefix file allowed Get-FileHash to complete; the a