# CVE-2021-20839: XML external entity in Office Server Document Converter

> Remote unauthenticated attackers can cause denial of service via XML External Entity attacks in Office Server Document Converter.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **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:** No
- **Published:** 1 Nov 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-gcx3-8mj9-xgm6

## What is CVE-2021-20839?

CVE-2021-20839 is a medium-severity vulnerability in Antenna House, Inc. Office Server Document Converter, published on 1 Nov 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

Office Server Document Converter V7.2MR4 and earlier and V7.1MR7 and earlier allows a remote unauthenticated attacker to conduct an XML External Entity (XXE) attack to cause a denial of service (DoS) condition to the other servers by processing a specially crafted XML document.

Weakness: CWE-611 (Improper Restriction of XML External Entity Reference)

## Which versions are affected by CVE-2021-20839?

It affects 1 product.


Products: Antennahouse Office Server Document Converter.

## How do I fix CVE-2021-20839?

No fix has been published for CVE-2021-20839 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-20839 being exploited?

There is no known exploitation of CVE-2021-20839 in the wild and no public exploit code.

## Other vulnerabilities in Antenna House, Inc. Office Server Document Converter

- [CVE-2018-3929](https://insights.sbomify.com/CVE-2018-3929/): Memory corruption in Antenna House (high 8.8)
- [CVE-2018-3930](https://insights.sbomify.com/CVE-2018-3930/): Memory corruption in Antenna House (high 8.8)
- [CVE-2018-3931](https://insights.sbomify.com/CVE-2018-3931/): Memory corruption in Antenna House (high 8.8)
- [CVE-2018-3932](https://insights.sbomify.com/CVE-2018-3932/): Memory corruption in Antenna House (high 8.8)
- [CVE-2018-3933](https://insights.sbomify.com/CVE-2018-3933/): Memory corruption in Antenna House (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20839 and fix it if it is affected.

What it is: CVE-2021-20839 is a medium-severity vulnerability in Antenna House, Inc. Office Server Document Converter, published on 1 Nov 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-2021-20839 in the wild and no public exploit code.

Affected product: Antenna House, Inc. Office Server Document Converter. 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-2021-20839/ (Markdown: https://insights.sbomify.com/CVE-2021-20839/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20839
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20839
- OSV: https://osv.dev/vulnerability/CVE-2021-20839

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-20839/
Summaries are generated and may contain mistakes; the official description above is the record.