# CVE-2021-21958: Memory corruption in Hancom

> A heap-based buffer overflow in Hancom Office allows attackers to execute arbitrary code via a specially crafted file.

- **Severity:** High 7.8 (`CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 16 Feb 2022
- **Updated:** 15 Apr 2025
- **Also known as:** GHSA-5fcw-h565-mjpq

## What is CVE-2021-21958?

CVE-2021-21958 is a high-severity memory corruption vulnerability in Hancom, published on 16 Feb 2022. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

A heap-based buffer overflow vulnerability exists in the Hword HwordApp.dll functionality of Hancom Office 2020 11.0.0.2353. A specially-crafted malformed file can lead to memory corruption and potential arbitrary code execution. An attacker can provide a malicious file to trigger this vulnerability.

Weakness: CWE-787 (Out-of-bounds Write), CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2021-21958?

It affects 1 product.


Products: Hancom Hancom Office 2020.

## How do I fix CVE-2021-21958?

No fix has been published for CVE-2021-21958 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21958 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-21958 exists.

## Other vulnerabilities in Hancom

- [CVE-2023-32541](https://insights.sbomify.com/CVE-2023-32541/): Use after free in Hancom Office 2020 (high 8.8)
- [CVE-2022-33896](https://insights.sbomify.com/CVE-2022-33896/): Memory corruption in Hancom Office 2020 (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21958 and fix it if it is affected.

What it is: CVE-2021-21958 is a high-severity memory corruption vulnerability in Hancom, published on 16 Feb 2022. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-21958 exists.

Affected product: Hancom. 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-2021-21958/ (Markdown: https://insights.sbomify.com/CVE-2021-21958/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21958
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21958
- OSV: https://osv.dev/vulnerability/CVE-2021-21958

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21958/
Summaries are generated and may contain mistakes; the official description above is the record.