CVE-2021-21390 | MITM modification of request bodies in MinIO

Exp

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.2021-03-17T02-33-02Z, there is a vulnerability which enables MITM modification of request bodies that are meant to have integrity guaranteed by chunk signatures. In a PUT request using aws-chunked encoding, MinIO ordinarily verifies signatures at the end of a chunk. This check can be skipped if the client sends a false chunk size that is much greater than the actual data sent: the server accepts and completes the request without ever reaching the end of the chunk + thereby without ever checking the chunk signature. This is fixed in version RELEASE.2021-03-17T02-33-02Z. As a workaround one can avoid using "aws-chunked" encoding-based chunk signature upload requests instead use TLS. MinIO SDKs automatically disable chunked encoding signature when the server endpoint is configured with TLS.

Published: 2021-03-19 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-21390 is rated High Exploit Risk (60.1/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.85%). 3 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-21390

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-21390

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.39% 0.85% +0.47%
2 2025-11-21 0.26% 0.39% +0.12%
3 2025-11-18 — 0.26% —

Full EPSS history (14 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-21390

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 3.6 [email protected]
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-21390

OS Trackers for CVE-2021-21390

vendor priority summary link
alpine medium CVE-2021-21390: 1 source package rows (minio); 190 state rows across 7 repos (3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.22-community, 3.23-community, edge-community); fixed 0, open 190. https://security.alpinelinux.org/vuln/CVE-2021-21390

Affected software / configurations for CVE-2021-21390

Vendor Product Version Raw CPE
minio minio < 2021-03-17t02-33-02z cpe:2.3:a:minio:minio:*:*:*:*:*:*:*:*

References for CVE-2021-21390

cvelogic Threat Intelligence