CVE-2026-103028: SFTPGo source-side file-pattern filter bypass during copy operations

File pattern filters (denied_patterns / allowed_patterns) were evaluated on the destination of a copy only. A user holding the copy permission could copy a file denied by the filters to a permitted name and then read it. A recursive directory copy reproduced the contents of a restricted directory under a path where the filters do not deny them, and the hide policy was affected in the same way: a file reported as missing by stat and by directory listings could still be copied.