rclone before 1.74.4 Security Token Disclosure via HTTPS to HTTP Redirect

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

rclone before 1.74.4 fails to strip the X-Amz-Security-Token header when an S3 redirect changes scheme from HTTPS to HTTP on the same host. Attackers can intercept plaintext HTTP traffic to capture AWS STS session tokens sent in request headers.

Source published

25 Aug 2026 15:16:11 UTC

Source modified

28 Aug 2026 22:26:44 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 9.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS 3.1 · 3.1 CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

rclone before 1.74.4 fails to strip the X-Amz-Security-Token header when an S3 redirect changes scheme from HTTPS to HTTP on the same host. Attackers can intercept plaintext HTTP traffic to capture AWS STS session tokens sent in request headers.

Source published

Aug 25, 2026, 3:16:11 PM (timezone not stated)

Source modified

Aug 28, 2026, 10:26:44 PM (timezone not stated)

Observed here

11 Nov 2026 16:10:00 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 9.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

rclone before 1.74.4 fails to strip the X-Amz-Security-Token header when an S3 redirect changes scheme from HTTPS to HTTP on the same host. Attackers can intercept plaintext HTTP traffic to capture AWS STS session tokens sent in request headers.

Source published

25 Aug 2026 16:17:30 UTC

Source modified

10 Sep 2026 20:46:19 UTC

Observed here

25 Oct 2026 16:19:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 9.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 3.1 CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

## Vulnerability Details **File**: `backend/s3/s3.go` **Lines**: 1359-1380 (functions `s3CheckRedirect` / `s3RedirectCrossesHost`) ### Root Cause Commit `e7b1eb774` (released in v1.74.3) added a `CheckRedirect` policy for the S3 HTTP client whose purpose is to strip the `X-Amz-Security-Token` header (the AWS STS session token) whenever a redirect chain "crosses a host", so the token isn't forwarded to an unintended origin. `s3RedirectCrossesHost` decides this purely by comparing `url.URL.Host` (hostname[:port]); it never looks at `url.URL.Scheme`. A redirect that keeps the exact same host:port but changes the scheme from `https://` to `http://` therefore compares as "same host" and `X-Amz-Security-Token` is *not* stripped — it is sent again, this time over plaintext HTTP. ```go func s3RedirectCrossesHost(req *http.Request, via []*http.Request) bool { if len(via) == 0 { return false } host := via[0].URL.Host for _, redirect := range via[1:] { if redirect.URL.Host != host { return true } } return host != req.URL.Host } ``` ### Attack Scenario 1. The user configures an `s3` remote (or `--s3-endpoint` pointing at a self-hosted/third-party S3-compatible service) using temporary credentials that include an STS `session_token` (common for assumed-role / CI / Kubernetes IRSA setups). 2. The configured endpoint responds to a request with a 3xx redirect to the *same* host:port but with `http://` instead of `https://` (TLS-front misconfiguration, maintenance redirect, or a malicious/compromised storage provider trying to harvest the token). 3. rclone's S3 HTTP client follows the redirect and re-sends the request, including `X-Amz-Security-Token`, over the now-unencrypted connection to that same host. 4. Any passive observer on that now-plaintext network path can read the STS session token from the request headers. ### Impact Disclosure of the AWS STS session token (`X-Amz-Security-Token`) in cleartext for the remainder of its validity window. This is the exact class of leak that `e7b1eb774` was written to close — it just doesn't cover the scheme-downgrade axis of "crossing a host". ### Vulnerable Code ```go func s3RedirectCrossesHost(req *http.Request, via []*http.Request) bool { if len(via) == 0 { return false } host := via[0].URL.Host for _, redirect := range via[1:] { if redirect.URL.Host != host { return true } } return host != req.URL.Host } ``` ### Recommended Fix Also compare `URL.Scheme`, so a scheme downgrade on the same host is treated the same as a host change: ```go func s3RedirectCrossesHost(req *http.Request, via []*http.Request) bool { if len(via) == 0 { return false } scheme, host := via[0].URL.Scheme, via[0].URL.Host for _, redirect := range via[1:] { if redirect.URL.Host != host || redirect.URL.Scheme != scheme { return true } } return host != req.URL.Host || scheme != req.URL.Scheme } ``` ### Verification Added a unit test (`backend/s3/redirect_scheme_test.go`) that calls the real, unmodified `s3RedirectCrossesHost` / `s3CheckRedirect` with an `https://bucket.example.com` -> `http://bucket.example.com` redirect chain. On unpatched code (commit 16091ce365, current master / v1.74.3): - `s3RedirectCrossesHost` returns `false` - `s3CheckRedirect` leaves `X-Amz-Security-Token: SECRET-SESSION-TOKEN` intact on the outgoing (plaintext) request. ``` === RUN TestSchemeDowngradeNotDetectedAsCrossHost redirect_scheme_test.go:23: initial=https://bucket.example.com final=http://bucket.example.com s3RedirectCrossesHost=false --- PASS: TestSchemeDowngradeNotDetectedAsCrossHost (0.00s) ``` After applying the one-line fix above (also adding scheme comparison), the token is correctly stripped and all existing redirect tests (`TestClientRemovesSecurityTokenOnCrossHostRedirect`, `TestClientDoesNotRestoreSecurityTokenAfterCrossHostRedirect`, `TestClientKeepsSecurityTokenOnSameHostRedirect`, `TestClientStopsAfterTenRedirects`) continue to pass. A minimal fix commit is ready and can be pushed to a private fork once this report is acknowledged.

Source published

5 Aug 2026 20:43:11 UTC

Source modified

25 Sep 2026 14:25:42 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Publisher rating · LOW

S3 session token leakage on HTTPS to HTTP redirect in github.com/rclone/rclone

Source published

18 Aug 2026 16:38:10 UTC

Source modified

25 Sep 2026 14:25:42 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.