What’s Vulnerable › Vulnerabilities

CVE-2021-21362: Bypassing readOnly policy by creating a temporary 'mc share upload' URL

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-03-08 · updated 2026-06-17
• Weakness: CWE-285

Description

MinIO is an open-source high performance object storage service and it is API compatible with Amazon S3 cloud storage service. In MinIO before version RELEASE.2021-03-04T00-53-13Z it is possible to bypass a readOnly policy by creating a temporary 'mc share upload' URL. Everyone is impacted who uses MinIO multi-users. This is fixed in version RELEASE.2021-03-04T00-53-13Z. As a workaround, one can disable uploads with `Content-Type: multipart/form-data` as mentioned in the S3 API RESTObjectPOST docs by using a proxy in front of MinIO.

Affected products

• minio: before 2021-03-04t00-53-13z — fixed in 2021-03-04t00-53-13z

How to fix

Upgrade to a fixed version: minio 2021-03-04t00-53-13z. Check the vendor advisory for mitigations.

References

• https://github.com/minio/minio/commit/039f59b552319fcc2f83631bb421a7d4b82bc482
• https://github.com/minio/minio/pull/11682
• https://github.com/minio/minio/releases/tag/RELEASE.2021-03-04T00-53-13Z
• https://github.com/minio/minio/security/advisories/GHSA-hq5j-6r98-9m8v
• https://github.com/minio/minio/commit/039f59b552319fcc2f83631bb421a7d4b82bc482
• https://github.com/minio/minio/pull/11682
• https://github.com/minio/minio/releases/tag/RELEASE.2021-03-04T00-53-13Z
• https://github.com/minio/minio/security/advisories/GHSA-hq5j-6r98-9m8v

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