CVE-2021-21390Network attack vector

Object modification via deferred chunk-signature verification

Published Mar 19, 2021 · Updated Aug 3, 2024

Message-integrity failure in MinIO before RELEASE.2021-03-17T02-33-02Z allows man-in-the-middle attackers to alter S3 PUT bodies. The s3ChunkedReader returned aws-chunked payload bytes before reaching the declared chunk end, where signature verification occurred, so an overstated chunk size let the server accept unverified data. Exploitation requires interception of a non-TLS, signature-chunked upload and changes stored object content without disclosing data or interrupting service.

CVSS severity5.9
Medium
EPSS probability0.85%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Message-integrity failure in MinIO before RELEASE.2021-03-17T02-33-02Z allows man-in-the-middle attackers to alter S3 PUT bodies. The s3ChunkedReader returned aws-chunked payload bytes before reaching the declared chunk end, where signature verification occurred, so an overstated chunk size let the server accept unverified data. Exploitation requires interception of a non-TLS, signature-chunked upload and changes stored object content without disclosing data or interrupting service.

The record

CVE
CVE-2021-21390
Published
Mar 19, 2021
Updated
Aug 3, 2024
Vendor
MinIO
Product
MinIO
Classifications
CWE-924, T1565.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 19, 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

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Is a vulnerable build present?

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

  1. Affected versionversion=< RELEASE.2021-03-17T02-33-02Z

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

MinIO · MinIOversion=< RELEASE.2021-03-17T02-33-02Z

Published CVSS scores

5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
6.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-924Improper Enforcement of Message Integrity During Transmission in a Communication Channel
T1565.002Transmitted Data Manipulation

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

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Your stack

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