GHSA-qqqm-5547-774x: FileBrowser Quantum: Path traversal in public share PATCH allows file ops outside shared directory

publicPatchHandler in backend/http/public.go joins user-controlled fromPath and toPath body fields with the trusted d.share.Path BEFORE the downstream sanitizer runs. Because filepath.Join collapses .. segments during the join, the sanitizer in resourcePatchHandler never sees the traversal and the move/copy/rename operates on a path outside the shared directory. The same root-cause pattern was patched for the bulk DELETE endpoint as CVE-2026-44542 (GHSA-fwj3-42wh-8673), but the PATCH handler with the identical pattern was not updated.

A public share link with AllowModify=true is sufficient to exploit this. Anyone holding such a link can move, copy, or rename arbitrary files within the share owner’s source root.

Verified on commit 869b640 (HEAD of main as of 2026-05-07).