# CVE-2021-23180: Null dereference in htmldoc

> A null pointer dereference in htmldoc allows attackers to execute arbitrary code or cause denial of service via crafted input.

- **Severity:** High 7.8 (`CVSS:3.1/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:** Yes
- **Published:** 2 Mar 2022
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-23180, GHSA-77xx-wx8p-7pfj, UBUNTU-CVE-2021-23180, USN-5198-1

## What is CVE-2021-23180?

CVE-2021-23180 is a high-severity vulnerability in htmldoc, published on 2 Mar 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 flaw was found in htmldoc in v1.9.12 and before. Null pointer dereference in file_extension(),in file.c may lead to execute arbitrary code and denial of service.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-23180?

It affects 1 product.


Products: Htmldoc Project Htmldoc.

## How do I fix CVE-2021-23180?

Apply the vendor's patch.

## Is CVE-2021-23180 being exploited?

There is no known exploitation of CVE-2021-23180 in the wild and no public exploit code.

## Other vulnerabilities in htmldoc

- [CVE-2024-46478](https://insights.sbomify.com/CVE-2024-46478/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-45508](https://insights.sbomify.com/CVE-2024-45508/): Memory corruption in n/a (critical 9.8)
- [CVE-2021-23158](https://insights.sbomify.com/CVE-2021-23158/): Memory corruption in htmldoc (critical 9.8)
- [CVE-2021-23165](https://insights.sbomify.com/CVE-2021-23165/): Memory corruption in htmldoc (critical 9.8)
- [CVE-2021-34119](https://insights.sbomify.com/CVE-2021-34119/): Memory corruption in n/a (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-23180 and fix it if it is affected.

What it is: CVE-2021-23180 is a high-severity vulnerability in htmldoc, published on 2 Mar 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: There is no known exploitation of CVE-2021-23180 in the wild and no public exploit code.

Affected product: htmldoc. 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-2021-23180/ (Markdown: https://insights.sbomify.com/CVE-2021-23180/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-23180
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-23180
- OSV: https://osv.dev/vulnerability/CVE-2021-23180

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-23180/
Summaries are generated and may contain mistakes; the official description above is the record.