GHSA-h4mf-4v27-hggj

## 1. Summary

WebDAV's default redirect handling can replay Basic authorization and configured Cookie headers over plaintext HTTP after a same-host HTTPS-to-HTTP redirect. This was reproduced through the real backend. Unlike the low-impact STS token in rclone's published S3 redirect advisory, Basic passwords and session cookies are complete reusable credentials, supporting a High rating when they grant normal WebDAV read/write access.

The credible threat requires a legitimate endpoint, gateway, or accelerator to emit an unsafe redirect and an adjacent/on-path actor to observe the plaintext hop. A report should not rely on a malicious original WebDAV endpoint because that endpoint already receives the credentials.

## 2. Affected Assets & Attack Surface

- Backend configuration/authentication: `backend/webdav/webdav.go:127-139`, `170-206`, `440-530` - Shared redirect callback: `lib/rest/rest.go:218-231` - HTTP client: `fs/fshttp/http.go:311-329` - Credentials: Basic passwords, bearer authorization, SharePoint/session cookies, and configured secret headers - Confirmed affected version: `<= v1.74.0-240`

## 3. Technical Root Cause Analysis

`PreserveMethodRedirectFn` limits redirect count and restores the original method, but it does not reject a transport downgrade or compare the full origin tuple. The client therefore relies on Go's hostname-oriented sensitive-header forwarding rules. Those rules can preserve `Authorization` and Cookie on a same-host redirect even when the new scheme is plaintext HTTP.

## 4. Proof-of-Concept & Evidence

1. Configure the actual WebDAV backend with Basic credentials and a Cookie. 2. Have the TLS endpoint return `307 Temporary Redirect` to an HTTP listener on the same hostname and a different port. 3. rclone follows the redirect while preserving the WebDAV method. 4. The plaintext listener receives both the Basic `Authorization` value and Cookie.

## 5. Impact Assessment

An on-path observer can reuse the captured password, bearer token, or session cookie for the account's permitted WebDAV operations. Confidentiality, integrity, and availability impact depend on that account's permissions.

## 6. Remediation Guidance

- Reject every HTTPS-to-HTTP redirect before replay. - Forward authenticated requests by default only when scheme, hostname, and effective port are unchanged. - Strip authorization, cookies, proxy credentials, and configured secret headers on all other redirects. - Put necessary provider exceptions behind exact destination allowlists. - Cover `301`, `302`, `303`, `307`, and `308` in regression tests.