Auth bypass in Rustfs
CVE-2026-39360
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.
Vulnerability class: Broken Access Control
EPSS: 0.002 (10.3th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.
Affected products
- Rustfs — versions 1.0.0, < alpha.90
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-39360?
- CVE-2026-39360 is a medium-severity vulnerability in Rustfs, classified under Missing Authorization. CVSS score: 4.3/10. Published 2026-04-07.
- How severe is CVE-2026-39360?
- Medium severity. CVSS v3 base score is 4.3 out of 10.