rclone: Path traversal in serve s3 allows reading and overwriting root-level files

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/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 · score source

EPSS

• CVE-2026-79781: 0.30% estimated exploitation activity in the next 30 days; percentile 23.03 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary rclone serve s3 allows a client to read and write files at the root of the remote which would normally be inaccessible by using dot-dot path segments in the object key. It does not allow reading files outside of the root. A request such as GET /bucket/../root-secret.txt is handled as an object request for bucket "bucket", but rclone normalizes the backend path and reads root-secret.txt from the serve root. The same issue also allows overwriting root-level files with PUT. Details The affected component is rclone serve s3. Relevant source files: cmd/serve/s3/backend.go cmd/serve/s3/multipart.go cmd/serve/s3/list.go In cmd/serve/s3/backend.go, the S3 backend builds backend paths by joining the bucket name and object key with path.Join: fp := path.Join(bucketName, objectName) This pattern is used in object operations such as HeadObject, GetObject, PutObject, DeleteObject, and CopyObject. S3 object keys are opaque names and can legally contain dot-dot segments. However, path.Join…

Published by the source

5 Aug 2026, 20:27 UTC

Last modified by the source

25 Sep 2026, 14:25 UTC

Source last checked

26 Oct 2026, 15:28 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-8v25-v8p6-qf7v

2. Revision 3 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6189

4. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-8v25-v8p6-qf7v

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# Patch Next advisory brief: CVE-2026-79781

Advisory: rclone: Path traversal in serve s3 allows reading and overwriting root-level files
IDs: CVE-2026-79781, GHSA-8v25-v8p6-qf7v
Record: https://patchnext.com/advisories/cve-2026-79781 (revision 4, source checked 26 Oct 2026, 15:28 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/rclone/rclone 1.74.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/rclone/rclone: affected <= 1.74.3; fixed in 1.74.4

## Suggested inspection (read-only)
- Go github.com/rclone/rclone: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/rclone/rclone.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-8v25-v8p6-qf7v (OSV record GHSA-8v25-v8p6-qf7v lists affected ranges: Go github.com/rclone/rclone >=0 <1.74.4 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6189 (OSV record GO-2026-6189 lists affected ranges: Go github.com/rclone/rclone >=0 <1.74.4 (fixed))
- Verified: https://github.com/advisories/GHSA-8v25-v8p6-qf7v (GitHub-reviewed advisory GHSA-8v25-v8p6-qf7v lists affected ranges: Go github.com/rclone/rclone >=0 <=1.74.3)

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