# CVE-2021-31207: Microsoft Exchange Server Security Feature Bypass

> Attackers can bypass security features in Microsoft Exchange Server, potentially facilitating further exploitation or unauthorized access.

- **Severity:** Medium 6.6 (`CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **Exploited in the wild:** Yes, since 3 Nov 2021 (CISA KEV), used in ransomware
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 May 2021
- **Updated:** 21 Oct 2025
- **Also known as:** GHSA-jcxv-6f65-7hrx

## What is CVE-2021-31207?

CVE-2021-31207 is a medium-severity vulnerability in Microsoft Exchange Server, published on 11 May 2021. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Microsoft Exchange Server Security Feature Bypass Vulnerability

Weakness: CWE-434 (Unrestricted Upload of File with Dangerous Type)

## Which versions are affected by CVE-2021-31207?

It affects 1 product.


Products: Microsoft Exchange Server.

## How do I fix CVE-2021-31207?

No fix has been published for CVE-2021-31207 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 17 Nov 2021.

## Is CVE-2021-31207 being exploited?

Yes. Attackers have exploited CVE-2021-31207 in the wild since at least 3 Nov 2021, including in ransomware campaigns.

Public exploit code:

- Microsoft Exchange ProxyShell RCE (metasploit)

## Other vulnerabilities in Microsoft Exchange Server

- [CVE-2024-21410](https://insights.sbomify.com/CVE-2024-21410/): Microsoft Exchange Server Privilege Escalation (critical 9.8, exploited in the wild)
- [CVE-2021-34473](https://insights.sbomify.com/CVE-2021-34473/): Microsoft Exchange Server Remote Code Execution (critical 9.1, exploited in the wild)
- [CVE-2021-26855](https://insights.sbomify.com/CVE-2021-26855/): Microsoft Exchange Server Remote Code Execution (critical 9.1, exploited in the wild)
- [CVE-2021-34523](https://insights.sbomify.com/CVE-2021-34523/): Microsoft Exchange Server Privilege Escalation (critical 9.0, exploited in the wild)
- [CVE-2023-21529](https://insights.sbomify.com/CVE-2023-21529/): Microsoft Exchange Server Deserialization of Untrusted Data (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-31207 and fix it if it is affected.

What it is: CVE-2021-31207 is a medium-severity vulnerability in Microsoft Exchange Server, published on 11 May 2021. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2021-31207 in the wild since at least 3 Nov 2021, including in ransomware campaigns.

Affected product: Microsoft Exchange Server. 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-2021-31207/ (Markdown: https://insights.sbomify.com/CVE-2021-31207/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-31207
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-31207
- OSV: https://osv.dev/vulnerability/CVE-2021-31207

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-31207/
Summaries are generated and may contain mistakes; the official description above is the record.