rclone: http backend forwards custom/auth headers to a different host on redirect

rclone is a command-line program to sync files and directories to and from different cloud storage providers. From 1.49.0 until 1.75.1, the HTTP backend attaches headers configured through --http-headers or headers= to requests in backend/http/http.go, while its fshttp.NewClient client follows redirects without a backend-specific http.Client.CheckRedirect policy. A configured remote that redirects to another host can therefore cause custom secrets such as X-Api-Key to be resent to that untrusted destination, and a same-host HTTPS-to-HTTP redirect can expose Authorization or Cookie headers in cleartext. Listing, stat, download, mount, and serve operations can trigger the leak during normal use. This issue is fixed in version 1.75.1.

rclone is a command-line program to sync files and directories to and from different cloud storage providers. From 1.49.0 until 1.75.1, the HTTP backend attaches headers configured through --http-headers or headers= to requests in backend/http/http.go, while its fshttp.NewClient client follows redirects without a backend-specific http.Client.CheckRedirect policy. A configured remote that redirects to another host can therefore cause custom secrets such as X-Api-Key to be resent to that untrusted destination, and a same-host HTTPS-to-HTTP redirect can expose Authorization or Cookie headers in cleartext. Listing, stat, download, mount, and serve operations can trigger the leak during normal use. This issue is fixed in version 1.75.1.

rclone is a command-line program to sync files and directories to and from different cloud storage providers. From 1.49.0 until 1.75.1, the HTTP backend attaches headers configured through --http-headers or headers= to requests in backend/http/http.go, while its fshttp.NewClient client follows redirects without a backend-specific http.Client.CheckRedirect policy. A configured remote that redirects to another host can therefore cause custom secrets such as X-Api-Key to be resent to that untrusted destination, and a same-host HTTPS-to-HTTP redirect can expose Authorization or Cookie headers in cleartext. Listing, stat, download, mount, and serve operations can trigger the leak during normal use. This issue is fixed in version 1.75.1.

## Vulnerability Details **File**: `backend/http/http.go` **Lines**: 285 (client construction — no `CheckRedirect`), 505-510 (`addHeaders`, writes configured secret headers onto every request), 533-534 / 700-701 / 782-785 (`f.httpClient.Do(req)` used by List/stat/download) ### Root Cause The `http` backend lets a user attach arbitrary secret headers to every request via `--http-headers`/`headers=` (documented for authentication: `'"Cookie","name=value","Authorization","xxx"'`). The backend's HTTP client is built with `fshttp.NewClient(ctx)`, which never sets `http.Client.CheckRedirect`, so it falls back to Go's stdlib default redirect policy. Go's default policy only strips four header names (`Authorization`, `Www-Authenticate`, `Cookie`, `Cookie2`), and only when the redirect target's *host* differs from the original — every other configured header is copied to the redirect target unconditionally, regardless of host or scheme. Even the four protected names survive a same-host `https://` → `http://` downgrade, since Go only checks host equality, not scheme. Any redirect response from the configured remote — whether from server compromise, an open redirect, a CDN/mirror failover to a different domain, or a malicious server from the start — causes rclone to resend every configured secret header (and, for a scheme downgrade, `Authorization`/`Cookie` in cleartext) to the new destination. This is the exact vulnerability class already fixed for the `s3` backend (`9328763`/`7543a7a`, GHSA-8mxv-9xhp-86h4 and the `webdav` backend (`59b513b`, GHSA-h4mf-4v27-hggj, wiring `rest.RefuseHTTPSDowngradeRedirectFn`). `backend/http` was not touched by either fix. ### Vulnerable Code ```go // backend/http/http.go:285 client := fshttp.NewClient(ctx) // no CheckRedirect set ... f.httpClient = client // used by readDir / NewObject / Object.Open ``` ```go // backend/http/http.go:505-510 func addHeaders(req *http.Request, opt *Options) { for i := 0; i < len(opt.Headers); i += 2 { key := opt.Headers[i] value := opt.Headers[i+1] req.Header.Add(key, value) } } ``` ### Attack Scenario 1. User configures an `http` remote: `url=https://good.example.com/files/`, `headers=X-Api-Key,SECRET-TOKEN`. 2. At some point `good.example.com` returns a redirect whose `Location` points at a different host (compromise, open redirect, CDN change, or malice from the start). 3. User runs any operation (`ls`, `cat`, `copy`, `mount`, `serve`) against the remote. 4. rclone follows the redirect with the default client and resends `X-Api-Key: SECRET-TOKEN` to the new, untrusted destination. 5. The attacker's server captures the secret from the incoming request. ### Impact Exfiltration of API keys / bearer tokens / session cookies configured for one host, to any host the (trusted-at-configuration-time) remote later redirects to. All operations on the `http` backend (list, stat, download, mount, serve) are affected. No special rclone privileges or unusual user interaction are needed beyond a normal sync/list/copy once the redirect exists. ### Dynamic Confirmation Built rclone from source at `cfdc9d0` (current master, `v1.76.0-DEV`) and configured: ```ini [testhttp] type = http url = http://127.0.0.1:9090/ headers = X-Api-Key,SUPER-SECRET-TOKEN-abc123 ``` Server A (port 9090, the "configured" host) 302-redirects every request to Server B (port 9091, a different host). Running `rclone cat testhttp:file.txt` caused Server B — which was never configured with any credential — to receive: ``` Header: X-Api-Key: SUPER-SECRET-TOKEN-abc123 Header: Referer: http://127.0.0.1:9090/file.txt ``` rclone printed Server B's response body as if it were the real file, confirming the full stat→redirect→download round trip leaks the header and trusts the redirect target. ### Vulnerable Code / Fix A minimal fix (implemented, tested, and verified to close the leak while preserving redirect functionality) wires the client to `rest.RefuseHTTPSDowngradeRedirectFn` (already used by `webdav`) and strips the configured `opt.Headers` on any cross-host redirect: ```go client := fshttp.NewClient(ctx) client.CheckRedirect = redirectCheckFn(opt) ... func redirectCheckFn(opt *Options) func(req *http.Request, via []*http.Request) error { return func(req *http.Request, via []*http.Request) error { if err := rest.RefuseHTTPSDowngradeRedirectFn(req, via); err != nil { return err } if len(via) > 0 && req.URL.Host != via[0].URL.Host { for i := 0; i < len(opt.Headers); i += 2 { req.Header.Del(opt.Headers[i]) } } return nil } } ``` A regression test (`TestRedirectStripsHeadersOnHostChange`) was added to `backend/http/http_internal_test.go`, confirmed to fail without the fix and pass with it. Full `backend/http` and `lib/rest` test suites pass with the fix applied. I have a fix branch ready to push to a private fork once this report is acknowledged. ### Verification Dynamically confirmed on rclone master @ `cfdc9d0` (post `v1.75.0`) in a local test harness — see "Dynamic Confirmation" above. Fix verified to eliminate the leak via the same harness (secret header absent from Server B after the fix; functionality — file download via redirect — unaffected).

rclone: http backend forwards custom/auth headers to a different host on redirect in github.com/rclone/rclone