# CVE-2021-21390: MITM modification of request bodies in MinIO

> Attackers can modify request bodies during transmission by bypassing chunk signature verification in MinIO object storage.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 19 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-xr7r-7gpj-5pgp, MINI-hm38-f53w-6r44, MINI-w4qj-66qm-r7xw

## What is CVE-2021-21390?

CVE-2021-21390 is a medium-severity vulnerability in minio, published on 19 Mar 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.2021-03-17T02-33-02Z, 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.

Weakness: CWE-924 (Improper Enforcement of Message Integrity During Transmission in a Communication Channel)

## Which versions are affected by CVE-2021-21390?

It affects 1 product.


Products: Minio Minio.

## How do I fix CVE-2021-21390?

Upgrade to a fixed version.

## Is CVE-2021-21390 being exploited?

There is no known exploitation of CVE-2021-21390 in the wild and no public exploit code.

## Other vulnerabilities in minio

- [CVE-2023-28434](https://insights.sbomify.com/CVE-2023-28434/): MinIO Security Feature Bypass (high 8.8, exploited in the wild)
- [CVE-2023-28432](https://insights.sbomify.com/CVE-2023-28432/): MinIO Information Disclosure (high 7.5, exploited in the wild)
- [CVE-2020-11012](https://insights.sbomify.com/CVE-2020-11012/): Authentication bypass MinIO Admin API (critical 9.3)
- [CVE-2026-33322](https://insights.sbomify.com/CVE-2026-33322/): MinIO: JWT Algorithm Confusion in OIDC Authentication (critical 9.2)
- [CVE-2026-33419](https://insights.sbomify.com/CVE-2026-33419/): MinIO: LDAP login brute-force via user enumeration and missing rate limit (critical 9.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21390 and fix it if it is affected.

What it is: CVE-2021-21390 is a medium-severity vulnerability in minio, published on 19 Mar 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-21390 in the wild and no public exploit code.

Affected product: minio. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-21390/ (Markdown: https://insights.sbomify.com/CVE-2021-21390/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21390
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21390
- OSV: https://osv.dev/vulnerability/CVE-2021-21390

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21390/
Summaries are generated and may contain mistakes; the official description above is the record.