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

Not scored Published 7 Sep 2021

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

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

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:

```
\end{CodeBlock}

\immediate\write18{COMMAND &gt; 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:

const escaped = content.replace(new RegExp(&#39;\\\\end\\s*{CodeBlock}&#39;, &#39;g&#39;), &#39;&#39;)

For more information

If you have any questions or comments about this advisory, open an issue in ZMarkdown.

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

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

Package	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.

Upgrade, and pass arguments to programs as a list instead of through a shell. More about Command injection.

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.