CVE-2021-21362Public exploitNetwork attack vector

Unauthorized object writes via missing policy enforcement

Published Mar 8, 2021 · Updated Aug 3, 2024

Improper authorization in MinIO before RELEASE.2021-03-04T00-53-13Z allows remote authenticated users to write objects despite read-only policy. PostPolicyBucketHandler validates the multipart POST signature but fails to check whether the signing user has PutObject permission for the bucket and object. A multi-user account with read-only access can create a temporary upload URL and use it to add an object, without reported read, delete, or availability impact.

CVSS severity7.7
High
EPSS probability1.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper authorization in MinIO before RELEASE.2021-03-04T00-53-13Z allows remote authenticated users to write objects despite read-only policy. PostPolicyBucketHandler validates the multipart POST signature but fails to check whether the signing user has PutObject permission for the bucket and object. A multi-user account with read-only access can create a temporary upload URL and use it to add an object, without reported read, delete, or availability impact.

The record

CVE
CVE-2021-21362
Published
Mar 8, 2021
Updated
Aug 3, 2024
Vendor
MinIO
Product
MinIO
Classifications
CWE-863, CWE-285, T1565.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< RELEASE.2021-03-04T00-53-13Z

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MinIO · MinIOversion=< RELEASE.2021-03-04T00-53-13Z

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:P/A:N
7.7GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-863Incorrect Authorization
CWE-285Improper Authorization
T1565.001Stored Data Manipulation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo