RustFS has an authorization bypass in multipart UploadPartCopy enables cross-bucket object exfiltration

Exploitation

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

CVSS 4.0

5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-39360: 0.20% estimated exploitation activity in the next 30 days; percentile 10.10 (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.

RustFS contains a missing authorization check in the multipart copy path (UploadPartCopy). A low-privileged user who cannot read objects from a victim bucket can still exfiltrate victim objects by copying them into an attacker-controlled multipart upload and completing the upload. This breaks tenant isolation in multi-user / multi-tenant deployments. Impact Unauthorized cross-bucket / cross-tenant data exfiltration (Confidentiality: High). An attacker with only minimal permissions on their own bucket (multipart upload + Put/Get on destination objects) can copy and retrieve objects from a victim bucket without having s3:GetObject (or equivalent) permission on the source. In the attached PoC, the attacker successfully exfiltrates a 5MB private object and proves integrity via matching SHA256 and size. Threat Model (Realistic) - Victim tenant/user owns a bucket (e.g., victim-bucket-) and stores private objects (e.g., private/financedump.bin). - Attacker tenant/user has no permissions on…

Published by the source

8 Apr 2026, 00:15 UTC

Last modified by the source

10 Apr 2026, 21:33 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-mx42-j6wv-px98

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# Patch Next advisory brief: CVE-2026-39360

Advisory: RustFS has an authorization bypass in multipart UploadPartCopy enables cross-bucket object exfiltration
IDs: CVE-2026-39360, GHSA-mx42-j6wv-px98
Record: https://patchnext.com/advisories/cve-2026-39360 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io rustfs: affected <= 0.0.2

## Suggested inspection (read-only)
- crates.io rustfs: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on rustfs.
- 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://github.com/advisories/GHSA-mx42-j6wv-px98 (GitHub-reviewed advisory GHSA-mx42-j6wv-px98 lists affected ranges: crates.io rustfs >=0 <=0.0.2)

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