# GHSA-2c83-wfv3-q25f: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') in ZMarkdown

> Attackers can execute arbitrary system commands via malicious Markdown input in the rebber module, affecting users of the ZMarkdown library.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Sep 2021

## What is GHSA-2c83-wfv3-q25f?

GHSA-2c83-wfv3-q25f is a command injection vulnerability in rebber, published on 7 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

### Impact

A Remote Command Execution vulnerability was found in the rebber module,
which allowed execution of arbitrary commands. The reported problem came
from CodeBlocks, which could be escaped to insert malicious LaTeX.

Anyone using `rebber` without sanitation of code content or a custom
macro is impacted by this vulnerability. Here is an example of a Markdown
content that will exploit the vulnerability:

````markdown
```
\end{CodeBlock}

\immediate\write18{COMMAND > outputrce}
\input{outputrce}

\begin{CodeBlock}{text}
```
````

Will insert into the generated LaTeX the result of executing
`COMMAND` on the system.

### Patches

The vulnerability has been patched in version 5.2.1.
If impacted, you should update to this version as soon as possible.

### Workarounds

It is possible to mitigate the vulnerability without upgrading by using a
custom code macro. Please make sure this custom macro escapes your
closing LaTeX sequence. For the example above, use:

```javascript
const escaped = content.replace(new RegExp('\\\\end\\s*{CodeBlock}', 'g'), '')
```

### For more information

If you have any questions or comments about this advisory, open an issue in [ZMarkdown](https://github.com/zestedesavoir/zmarkdown/issues).

## Which versions are affected by GHSA-2c83-wfv3-q25f?

2 open source packages ship an affected version, including rebber.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `rebber` | npm | All versions | 5.2.1 |
| `rebber` | npm | All versions | 5.2.1 |

## How do I fix GHSA-2c83-wfv3-q25f?

Upgrade rebber to 5.2.1 or later.

## Is GHSA-2c83-wfv3-q25f being exploited?

There is no known exploitation of GHSA-2c83-wfv3-q25f in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-2c83-wfv3-q25f and fix it if it is affected.

What it is: GHSA-2c83-wfv3-q25f is a command injection vulnerability in rebber, published on 7 Sep 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 GHSA-2c83-wfv3-q25f in the wild and no public exploit code.

Affected packages and fixed versions:
- rebber (npm): affected all versions; fixed in 5.2.1
- rebber (npm): affected all versions; fixed in 5.2.1

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/GHSA-2c83-wfv3-q25f/ (Markdown: https://insights.sbomify.com/GHSA-2c83-wfv3-q25f/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-2c83-wfv3-q25f

---
From sbomify Insights: https://insights.sbomify.com/GHSA-2c83-wfv3-q25f/
Summaries are generated and may contain mistakes; the official description above is the record.