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

> Attackers can bypass read-only policies in MinIO by generating temporary upload URLs, allowing unauthorized data modification.

- **Severity:** High 7.7 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-hq5j-6r98-9m8v, MINI-8q66-wv8v-5pww, MINI-fgpm-38vg-2j6g

## What is CVE-2021-21362?

CVE-2021-21362 is a high-severity vulnerability in minio, published on 8 Mar 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### 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.2021-03-04T00-53-13Z 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.

Weakness: CWE-863 (Incorrect Authorization), CWE-285 (Improper Authorization)

## Which versions are affected by CVE-2021-21362?

It affects 1 product.


Products: Minio Minio.

## How do I fix CVE-2021-21362?

Upgrade to a fixed version.

## Is CVE-2021-21362 being exploited?

There is no known exploitation of CVE-2021-21362 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-2021-21362 and fix it if it is affected.

What it is: CVE-2021-21362 is a high-severity vulnerability in minio, published on 8 Mar 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-21362 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-2021-21362/ (Markdown: https://insights.sbomify.com/CVE-2021-21362/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21362
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21362
- OSV: https://osv.dev/vulnerability/CVE-2021-21362

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21362/
Summaries are generated and may contain mistakes; the official description above is the record.