FontForge is a popular, open-source font editor used by designers and developers worldwide to edit and create fonts. Recently, a security vulnerability surfaced that could let attackers take over your machine—just by tricking you into opening a malicious file in FontForge. Let’s take a simple but deep look at CVE-2024-25082, how and why it works, and what you can do about it.

What’s CVE-2024-25082 All About?

In FontForge through version 20230101, a component called *Splinefont* contains a command injection vulnerability. If you open a specially crafted archive or compressed font file, an attacker can make your computer run hidden, unwanted commands. This could let them install malware, steal files, or control your system—all without you knowing.

- NIST National Vulnerability Database Entry
- Original FontForge Commit Discussions

How Does the Exploit Work? Simple Explanation

FontForge supports opening and extracting fonts from ZIP or TAR archives, and even compressed files like GZ or BZ2. Unfortunately, when handling these files, the *Splinefont* code used system commands without properly checking (sanitizing) file names. If a file inside the archive has a sneaky, malicious name, FontForge could run system-level commands encoded in it.

Example:
If an attacker tricks you into opening a font archive with a file name like myfont.sfd;rm -rf ~/.local/*;, FontForge might process it, but the semicolon (;) tells the shell to run the following command—in this case, to delete all your local files!

Here’s a simple Python snippet that creates a hostile archive

import tarfile

# This filename will *also* run a shell command if blindly passed to 'tar' using shell=True
malicious_name = "evilfont.sfd;touch HACKED_BY_CVE25082;"
with tarfile.open('exploit.tar', 'w') as tar:
    tarinfo = tarfile.TarInfo(name=malicious_name)
    tarinfo.size = 1
    tar.addfile(tarinfo)

Now, if a vulnerable FontForge extracts and opens this archive, the touch HACKED_BY_CVE25082 command will run—creating a file called “HACKED_BY_CVE25082” on your machine!

Remote Code Execution: Untrusted font files can run commands on your system.

- Cross-Platform: Both Windows, Mac, and Linux versions are affected (since FontForge is cross-platform and often calls system utilities).
- No Warning: Victims won’t know unless they spot something odd later, like missing or altered files.

How to Stay Safe

- Update FontForge to the *latest* version. Versions after 20230101 have patched this issue. Download here.
- Be cautious with font files from strangers—just like you wouldn’t open every email attachment you get.
- Don’t run FontForge as admin/root unless you must. Keep your privileges low!
- Check for Hacked Files: If you opened strange fonts, look for odd files or changes in your folders.

Here’s a peek at the old, vulnerable code pattern (simplified)

// ... inside FontForge source Splinefont.c
sprintf(cmd, "tar -xf %s", archive_name);
system(cmd); // dangerous: runs whatever is in archive_name!

Careless use of system() and sprintf() with unsanitized user input is a classic recipe for command injection bugs!

Final Thoughts

Font files are usually harmless—but in the age of hacking, even creative tools like FontForge aren’t immune to attack. CVE-2024-25082 shows how quickly a neat feature (automatic extraction) can backfire if security isn’t top priority. If you use FontForge, update it now, and remember: don’t trust fonts from people you don’t trust!

---
Stay updated and always be careful with third-party files. For more in-depth details, check the official NVD entry.

Timeline

Published on: 02/26/2024 16:27:58 UTC
Last modified on: 11/04/2024 19:35:04 UTC