rclone before v1.75.0 Credential Exposure via S3 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 v1.75.0 fails to sanitize IBM IAM bearer tokens and SSE-C encryption keys during S3 redirect callbacks, allowing credentials to be preserved across scheme or host changes. Attackers observing network traffic from a trusted endpoint can capture reusable IBM IAM tokens on same-host HTTPS-to-HTTP downgrades or SSE-C keys on cross-origin redirects to access protected S3 objects.

Source published

25 Aug 2026 15:16:09 UTC

Source modified

25 Aug 2026 16:07:21 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 · 6.0 CVSS:4.0/AV:A/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

CVSS 3.1 · 5.3 CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

rclone before v1.75.0 fails to sanitize IBM IAM bearer tokens and SSE-C encryption keys during S3 redirect callbacks, allowing credentials to be preserved across scheme or host changes. Attackers observing network traffic from a trusted endpoint can capture reusable IBM IAM tokens on same-host HTTPS-to-HTTP downgrades or SSE-C keys on cross-origin redirects to access protected S3 objects.

Source published

Aug 25, 2026, 3:16:09 PM (timezone not stated)

Source modified

Aug 25, 2026, 4:07:21 PM (timezone not stated)

Observed here

11 Nov 2026 16:09:57 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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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 · 6.0 CVSS:4.0/AV:A/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

rclone before v1.75.0 fails to sanitize IBM IAM bearer tokens and SSE-C encryption keys during S3 redirect callbacks, allowing credentials to be preserved across scheme or host changes. Attackers observing network traffic from a trusted endpoint can capture reusable IBM IAM tokens on same-host HTTPS-to-HTTP downgrades or SSE-C keys on cross-origin redirects to access protected S3 objects.

Source published

25 Aug 2026 16:17:29 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

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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 · 6.0 CVSS:4.0/AV:A/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/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 · 5.3 CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

## 1. Summary The S3 redirect callback strips `X-Amz-Security-Token` when a redirect changes scheme or host, but it does not strip IBM IAM bearer authorization or customer-provided encryption keys. Two independently validated paths remain: - a same-host HTTPS-to-HTTP redirect preserves `Authorization: Bearer ...` and exposes a reusable IBM IAM token to the plaintext network path; - a cross-origin redirect preserves SSE-C and copy-source SSE-C key headers. The High rating is driven by the reusable IBM IAM bearer token. The SSE-C cross-origin disclosure is a secondary confidentiality issue. The meaningful threat is a trusted endpoint, gateway, or accelerator that emits an unsafe redirect, followed by an adjacent/on-path observer; describing the originally configured endpoint itself as the attacker would be weak because that endpoint already receives the request secrets. ## 2. Affected Assets & Attack Surface - S3 redirect policy: `backend/s3/s3.go:1345-1379` - IBM IAM signer: `backend/s3/ibm_signer.go:28-40` - SSE-C key preparation: `backend/s3/s3.go:1821-1837` - Affected operations: requests carrying IBM IAM authorization, SSE-C keys, or copy-source SSE-C keys - Confirmed affected version: `<= v1.74.0-240-ga0c09f138` ## 3. Technical Root Cause Analysis `s3CheckRedirect` applies a one-header denylist: ```go if s3RedirectCrossesHost(req, via) { req.Header.Del("X-Amz-Security-Token") } ``` Go removes `Authorization` on some hostname changes, but preserves it for a same-host redirect and does not treat a scheme downgrade as sufficient reason to remove it. Go also has no generic knowledge that the SSE-C headers contain raw encryption keys. The rclone callback recognizes the STS token but not these additional origin-bound secrets. ## 4. Proof-of-Concept & Evidence Using the actual redirect callback: 1. An HTTPS endpoint redirected to HTTP on the same hostname. 2. The plaintext destination received the planted IBM bearer token and SSE-C headers. 3. A separate redirect to an unrelated hostname caused Go to remove `Authorization`, but the destination still received both SSE-C key headers. 4. In both cases, rclone removed the planted STS token, proving that the S3-specific callback executed while omitting the other secret classes. The related [GHSA-gx4c-2hqx-cw2r](https://github.com/rclone/rclone/security/advisories/GHSA-gx4c-2hqx-cw2r) covers the STS downgrade path and confirms that rclone treats scheme changes as a credential boundary. It does not cover the IBM bearer or SSE-C variants retained here. ## 5. Impact Assessment A captured IBM bearer token can authorize reads, writes, and deletes within its IAM scope. A disclosed SSE-C key can expose corresponding ciphertext available to the recipient; copy-source keys can expose protected source objects. The exact impact is limited by token policy and the attacker's access to encrypted objects. ## 6. Remediation Guidance - Reject every HTTPS-to-HTTP redirect before replay. - Do not automatically follow secret-bearing cross-origin redirects. - On any scheme, host, or effective-port change, remove all authorization, cookies, session tokens, SSE-C fields, copy-source SSE-C fields, and provider-specific credentials. - Where redirects are required, allowlist exact destinations and reconstruct/re-sign a new request. - Add redirect tests for every secret header class and for scheme, hostname, subdomain, and port changes.

Source published

5 Aug 2026 20:27:50 UTC

Source modified

25 Sep 2026 14:25:35 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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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:H/I:N/A:N

Publisher rating · MODERATE

S3 redirect sanitization omits sensitive headers in github.com/rclone/rclone

Source published

18 Aug 2026 16:38:10 UTC

Source modified

25 Sep 2026 14:25:35 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.