{"id":"CVE-2026-79780","aliases":["BIT-rclone-2026-79780","GHSA-8mxv-9xhp-86h4","GO-2026-6188"],"url":"https://o3.security/vulnerability/CVE-2026-79780","summary":"rclone before v1.75.0 Credential Exposure via S3 Redirect","details":"## 1. Summary\n\nThe 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:\n\n- a same-host HTTPS-to-HTTP redirect preserves `Authorization: Bearer ...` and exposes a reusable IBM IAM token to the plaintext network path;\n- a cross-origin redirect preserves SSE-C and copy-source SSE-C key headers.\n\nThe 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.\n\n## 2. Affected Assets & Attack Surface\n\n- S3 redirect policy: `backend/s3/s3.go:1345-1379`\n- IBM IAM signer: `backend/s3/ibm_signer.go:28-40`\n- SSE-C key preparation: `backend/s3/s3.go:1821-1837`\n- Affected operations: requests carrying IBM IAM authorization, SSE-C keys, or copy-source SSE-C keys\n- Confirmed affected version: `<= v1.74.0-240-ga0c09f138`\n\n## 3. Technical Root Cause Analysis\n\n`s3CheckRedirect` applies a one-header denylist:\n\n```go\nif s3RedirectCrossesHost(req, via) {\n    req.Header.Del(\"X-Amz-Security-Token\")\n}\n```\n\nGo 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.\n\n## 4. Proof-of-Concept & Evidence\n\nUsing the actual redirect callback:\n\n1. An HTTPS endpoint redirected to HTTP on the same hostname.\n2. The plaintext destination received the planted IBM bearer token and SSE-C headers.\n3. A separate redirect to an unrelated hostname caused Go to remove `Authorization`, but the destination still received both SSE-C key headers.\n4. In both cases, rclone removed the planted STS token, proving that the S3-specific callback executed while omitting the other secret classes.\n\nThe 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.\n\n## 5. Impact Assessment\n\nA 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.\n\n## 6. Remediation Guidance\n\n- Reject every HTTPS-to-HTTP redirect before replay.\n- Do not automatically follow secret-bearing cross-origin redirects.\n- 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.\n- Where redirects are required, allowlist exact destinations and reconstruct/re-sign a new request.\n- Add redirect tests for every secret header class and for scheme, hostname, subdomain, and port changes.","published":"2026-08-25T15:16:09.789Z","modified":"2026-10-28T02:30:24.847157102Z","cvss":null,"epss":{"score":0.00095,"percentile":0.00764,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/rclone/rclone","fixedVersion":"1.75.0"}],"fix":{"url":"https://github.com/rclone/rclone/commit/7543a7a87884aca957590b20b0714078d51af87b","label":"rclone/rclone@7543a7a"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/79xxx/CVE-2026-79780.json"},{"type":"ADVISORY","url":"https://github.com/rclone/rclone/security/advisories/GHSA-8mxv-9xhp-86h4"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-79780"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/rclone-before-credential-exposure-via-s3-redirect"},{"type":"WEB","url":"https://github.com/rclone/rclone/commit/7543a7a87884aca957590b20b0714078d51af87b"},{"type":"WEB","url":"https://github.com/rclone/rclone/commit/9328763d1b73db71e97c0332b19e3747abeb9191"},{"type":"PACKAGE","url":"https://github.com/rclone/rclone"},{"type":"WEB","url":"https://github.com/rclone/rclone/releases/tag/v1.75.0"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:24.847157102Z"}}