In March 2022, security researchers found a dangerous vulnerability in the widely used libtiff library. This flaw, labeled CVE-2022-0909, could allow attackers to crash applications just by getting them to process a specially-crafted TIFF image. Even if this doesn't allow remote code execution, it can cause denial-of-service (DoS), making it a significant risk for any system handling image files. In this post, we will break down what the problem is, how to understand the code behind it, and what you can do to protect your projects.

What is libtiff and tiffcrop?

libtiff is a powerful open-source C library for reading, writing, and manipulating TIFF (Tagged Image File Format) images. Many image editors, graphics software, and even document scanners depend on libtiff behind the scenes.

tiffcrop is a command-line tool bundled with libtiff. It helps crop and manipulate TIFF images. If tiffcrop crashes or gets exploited, any server or application that uses it could go down.

What is CVE-2022-0909?

CVE-2022-0909 is a vulnerability in tiffcrop found in libtiff version 4.3.. The root cause is a *divide by zero* bug in the code. If an attacker crafts a TIFF file with specific metadata (like image height or width set to zero), running tiffcrop on it will cause the program to try to divide by zero, crashing immediately.

The danger? If an attacker uploads an image or attaches it to an email, any automated process (like a thumbnail generator) could fall victim.

Vulnerable Code Details

The vulnerability lies in the function that processes TIFF images. Here's a simplified example inspired by the real code:

// Imagine this code in tiffcrop.c
int nrows = ... // value read from the file, attacker sets this to 
int stripsize = scanline_size / nrows; // risky: could divide by zero here

If nrows is zero—something that should never happen, but a malicious TIFF could set it—the division fails and the program crashes.

Original Patch:
The fix checks if nrows is zero before dividing.  
See the commit here:  
https://gitlab.com/libtiff/libtiff/-/commit/f8df9aa

Snippet from the actual fix

if (nrows == ) {
    TIFFError("tiffcrop", "Number of rows is zero. Invalid TIFF file.");
    exit(EXIT_FAILURE);
}
int stripsize = scanline_size / nrows;

Exploit Example

Here's a minimal example of how an attacker could create a malicious TIFF file using Python's Pillow library (for research purposes only):

from PIL import Image
import numpy as np

# Create a zero-height image (invalid but possible to write)
arr = np.zeros((, 10, 3), dtype=np.uint8)
im = Image.fromarray(arr)
im.save("crash.tiff")

Now, if a vulnerable tiffcrop processes crash.tiff, it'll trigger the divide by zero and crash.

Or, as a file fuzzing illustration, you can hex-edit a valid TIFF and set the height field (at offset x118 for some files) to zero.

Note: Never run suspicious files on production systems!

If you compile from source

- Download the latest libtiff source from official releases.
- Or, if you need the fix only, apply commit f8df9aa.

You can patch your code with

  git clone https://gitlab.com/libtiff/libtiff.git
  cd libtiff
  git checkout f8df9aa
  ./configure
  make && sudo make install

Further References

- libtiff Security Advisories
- CVE-2022-0909 at NVD
- Patch commit f8df9aa

Conclusion

CVE-2022-0909 is a classic but critical example of why input validation matters. Even tiny math mistakes can take down important servers and systems if they handle bad input from the outside world. If you develop or deploy software that touches TIFF files, update your libtiff to at least 4.3. with the *divide by zero* patch. Even a small file can cause big problems!

Stay safe, keep your dependencies updated, and always validate external data.

*Feel free to share or link to this article. For more how-to security breakdowns, stay tuned!*

Timeline

Published on: 03/11/2022 18:15:00 UTC
Last modified on: 05/12/2022 20:04:00 UTC