GHSA-49h3-cwhj-4737

Описание

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:

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:

3. SuggestedTarget joined as a path — service/explorer/viewer.go:

4. JoinRaw splits on / and normalizes via url.JoinPath — pkg/filemanager/fs/uri.go:

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:

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:

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.