GHSA-49h3-cwhj-4737

## Summary Cloudreve's WOPI `PUT_RELATIVE` handler treats `X-WOPI-SuggestedTarget` as a path, not a filename. It splits the header on `/` and joins the segments onto the source file's directory with `URI.JoinRaw`, which feeds Go's `url.JoinPath`. `url.JoinPath` resolves `.`/`..` segments, so a slash-bearing target such as `a/../../evil.docx` collapses to a location outside the source file's directory. The lower-level upload path then validates only the final, already-cleaned basename (`evil.docx`), which is harmless, and checks ownership against the *resolved ancestor* — which is still the same user's drive. A WOPI access token is bound to exactly one file (the route enforces `fileId == session.FileID` with a 403 otherwise). `PUT_RELATIVE` escapes that per-file scope: a token issued for one file can create (and, conditionally, overwrite) files elsewhere in the same account.

## Root cause (verified at `26b6b10`) **1. Token is single-file scoped (the boundary being escaped)** — `middleware` `ViewerSessionValidation`: ```go fileId := hashid.FromContext(c) if fileId != session.FileID { // 403 — token is bound to ONE file c.Status(http.StatusForbidden); c.Abort(); return } ``` Route: `wopi := noAuth.Group("file/wopi", middleware.HashID(hashid.FileID), middleware.ViewerSessionValidation())`; `wopi.POST(":id", controllers.ModifyFile)` → `POST /api/v4/file/wopi/:id?access_token=<token>`. **2. `PUT_RELATIVE` dispatch** — `routers/controllers/wopi.go`: ```go case wopi.MethodPutRelative: // X-WOPI-Override: PUT_RELATIVE err = service.PutContent(c, true) ``` **3. SuggestedTarget joined as a path** — `service/explorer/viewer.go`: ```go fileName, _ := wopi.UTF7Decode(c.GetHeader(wopi.SuggestedTargetHeader)) // X-WOPI-SuggestedTarget fileUriParsed, _ := fs.NewUriFromString(fileUri) if strings.HasPrefix(fileName, ".") { /* treat as extension */ } fileUri = fileUriParsed.DirUri().JoinRaw(fileName).String() // <-- path join, not basename ... subService := FileUpdateService{ Uri: fileUri } res, err := subService.PutContent(c, lockSession) ``` **4. `JoinRaw` splits on `/` and normalizes via `url.JoinPath`** — `pkg/filemanager/fs/uri.go`: ```go func (u *URI) Join(elem ...string) *URI { newUrl, _ := url.Parse(u.U.String()) return &URI{U: newUrl.JoinPath(/* PathEscape each elem */ ...)} // JoinPath cleans ./ and ../ } func (u *URI) JoinRaw(elem string) *URI { return u.Join(strings.Split(strings.TrimPrefix(elem, Separator), Separator)...) } ``` `PathEscape` leaves `.` unescaped (it is in the unreserved set), so `..` segments survive into `JoinPath`, which resolves them. `URI.Name()` returns `path.Base(path.Clean(path))` — the cleaned basename. **5. Upload checks ownership of the resolved ancestor and validates only the clean basename** — `pkg/filemanager/fs/dbfs/upload.go`: ```go ancestor, err := f.getFileByPath(ctx, navigator, req.Props.Uri) // URI already traversal-normalized ... if _, ok := ctx.Value(ByPassOwnerCheckCtxKey{}).(bool); !ok && ancestor.OwnerID() != f.user.ID { return nil, fs.ErrOwnerOnly // same-user -> passes } ... if err := validateNewFile(req.Props.Uri.Name(), req.Props.Size, policy); err != nil { // checks "evil.docx" only return nil, err } ``` `validateFileName` rejects `/ \ : * ? " < > |` and bare `.`/`..` — but the traversal is already gone by the time it sees the basename.

## Validation performed Independent validation against commit `26b6b10` in a clean sandbox. **Source-verified (static):** the full chain confirmed verbatim — single-file-scoped token (403 on mismatch) → `PUT_RELATIVE` dispatch → `DirUri().JoinRaw(SuggestedTarget)` → `url.JoinPath` normalization → ancestor ownership check (same-user passes) → basename-only validation of the cleaned name. **Dynamic (control-flow executed):** the full binary is not buildable offline here (modules behind an unreachable Go proxy, embedded frontend, DB). I built and ran a harness using the **real Go `net/url` stdlib** plus the **verbatim** `Join`/`JoinRaw`/`DirUri`/`Path`/`Name`/`PathEscape`/`shouldEscape` and the `validateFileName` gate, driving the same transformation `PUT_RELATIVE` performs. Source = `cloudreve://my/folder/current.docx`: ``` SuggestedTarget resolved URI final basename validator "copy.docx" cloudreve://my/folder/copy.docx "copy.docx" ACCEPT "a/../../evil.docx" cloudreve://my/evil.docx "evil.docx" ACCEPT <- ESCAPED to / "a/../../../top.docx" cloudreve://my/top.docx "top.docx" ACCEPT <- ESCAPED to / "sub/evil.docx" cloudreve://my/folder/sub/evil.docx "evil.docx" ACCEPT <- different subdir ".pdf" cloudreve://my/folder/current.pdf "current.pdf" ACCEPT "a%2f..%2f..%2fenc.docx" cloudreve://my/folder/a%252f..%252f.. "a%2f..%2f..%2f" ACCEPT (NO escape) ``` The headline payload `a/../../evil.docx` deterministically resolves to `cloudreve://my/evil.docx` (account root) with a clean, accepted basename. Output matches the original audit probe exactly. Honest caveat: a leading non-`..` segment (e.g. `a/`) is required to prime the join; a single `../evil.docx` does not cleanly escape, and **URL-encoded separators (`%2f`) do not traverse** through this path (they are re-escaped into one literal segment). Only literal `/` separators work. **Confidence tier: source-verified + control-flow dynamically reproduced (no full live HTTP write against a deployed instance).** **Deduplication:** no existing CVE/GHSA matches. Known Cloudreve advisories are CVE-2022-32167 (XSS, v1–v3.5.3) and CVE-2026-25726 (weak-PRNG ATO, instances initialized < v4.10.0) — both unrelated. `SECURITY.md` lists "user permissions" as high-impact and in scope for all 4.x, so this qualifies as a vulnerability under the project's own policy. ## Steps to reproduce **Setup:** user owns `cloudreve://my/folder/current.docx`; open it in the WOPI editor to obtain `<token>` (the session is bound to that file's ID). 1. Send the crafted `PUT_RELATIVE`: ``` POST /api/v4/file/wopi/<file-id>?access_token=<token> HTTP/1.1 Host: target X-WOPI-Override: PUT_RELATIVE X-WOPI-SuggestedTarget: <UTF-7 of "a/../../evil.docx"> Content-Type: application/octet-stream <file bytes> ``` 2. Cloudreve rewrites the target from `cloudreve://my/folder/current.docx` to `cloudreve://my/evil.docx`, validates the basename `evil.docx` (passes), and writes the content. **Expected:** the target is rejected or constrained to the source file's directory. **Actual:** a file is written at the account root, outside the token's single-file scope. ## Impact A WOPI access token scoped to one file can write files to other locations in the same user's account. A malicious or compromised WOPI integration (or a leaked token) can plant or, conditionally, overwrite files at attacker-chosen paths the account owns, defeating the per-file scoping the WOPI session is meant to enforce. Confined to the session user's account (not cross-user). ## Remediation - Treat `X-WOPI-SuggestedTarget` (and `X-WOPI-RequestedName`) as a **filename**, not a path: reject `/`, `\`, dot segments, and percent-encoded separator variants before joining. - Prefer `DirUri().Join(sanitizedBaseName)` over `JoinRaw`, and after constructing the target URI assert it is a direct child of the source file's directory. - Add regression tests for `a/../../evil.docx`, `sub/evil.docx`, and encoded-separator variants.