# CVE-2021-21994: Auth bypass in VMware ESXi and VMware Cloud Foundation

> Attackers can bypass SFCB authentication in VMware ESXi by sending crafted requests to port 5989, requiring immediate patching.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Jul 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-4643-h6pq-84f9

## What is CVE-2021-21994?

CVE-2021-21994 is a critical authentication bypass vulnerability in Vmware Cloud Foundation, published on 13 Jul 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SFCB (Small Footprint CIM Broker) as used in ESXi has an authentication bypass vulnerability. A malicious actor with network access to port 5989 on ESXi may exploit this issue to bypass SFCB authentication by sending a specially crafted request.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2021-21994?

It affects 2 products.


Products: Vmware Cloud Foundation, Vmware Esxi.

## How do I fix CVE-2021-21994?

No fix has been published for CVE-2021-21994 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21994 being exploited?

There is no known exploitation of CVE-2021-21994 in the wild and no public exploit code.

Public exploit code:

- https://github.com/mreza-en/cve-2021-21994_POC (github_poc): https://github.com/mreza-en/cve-2021-21994_POC

## Other vulnerabilities in Vmware Cloud Foundation

- [CVE-2024-38812](https://insights.sbomify.com/CVE-2024-38812/): VMware vCenter Server Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-37079](https://insights.sbomify.com/CVE-2024-37079/): Broadcom VMware vCenter Server Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2022-22954](https://insights.sbomify.com/CVE-2022-22954/): VMware Workspace ONE Access and Identity Manager Server-Side Template Injection (critical 9.8, exploited in the wild)
- [CVE-2021-22005](https://insights.sbomify.com/CVE-2021-22005/): VMware vCenter Server File Upload (critical 9.8, exploited in the wild)
- [CVE-2021-21985](https://insights.sbomify.com/CVE-2021-21985/): VMware vCenter Server Improper Input Validation (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21994 and fix it if it is affected.

What it is: CVE-2021-21994 is a critical authentication bypass vulnerability in Vmware Cloud Foundation, published on 13 Jul 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-21994 in the wild and no public exploit code.

Affected product: Vmware Cloud Foundation. 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-2021-21994/ (Markdown: https://insights.sbomify.com/CVE-2021-21994/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21994
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21994
- OSV: https://osv.dev/vulnerability/CVE-2021-21994

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21994/
Summaries are generated and may contain mistakes; the official description above is the record.