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Introduction

LibTIFF is a widely-used open source library for handling TIFF image files. On December 24, 2022, a vulnerability known as CVE-2022-48281 was publicly disclosed. This flaw, present in LibTIFF versions up to 4.5., allows an attacker to cause a heap-based buffer overflow via a crafted TIFF image, potentially resulting in program crashes or code execution.

In this post, we'll take a deep dive into the vulnerability, looking at the root cause, how to reproduce it, and reference resources. We will keep everything simple and clear, with exclusive code snippets and guidance.

What is CVE-2022-48281?

The vulnerability lies in the processCropSelections function in tools/tiffcrop.c. If a specially crafted input TIFF file is provided, a boundary check fails to account for the real size required by cropping selections, leading to a heap-based buffer overflow.

Common triggers:

Images crafted with intentionally large crop selections

- Images designed to confuse row/column handling

Where Did LibTIFF Go Wrong?

The affected code is responsible for cropping TIFF images based on provided selections. Let's look at the vulnerable section of code (simplified):

// processCropSelections snippet
if ((crop->crop_mode & CROP_SECTIONS) != )
{
    /* Allocate buffer for selections */
    crop->regionlist = _TIFFmalloc(sizeof(struct region) * crop->selections);
    for (i = ; i < crop->selections; i++) {
        /* Accessing memory based on user-controlled 'selections' value */
        crop->regionlist[i] = ...; // Details determined by the input
    }
}

The issue is that there is no proper boundary check for the number of selections. If a TIFF file specifies a very high number here, the code allocates too little memory or the attacker can manipulate the structure's content, causing a buffer overrun.

Attacker crafts a TIFF image with a selections field set to a massive number.

2. The image is parsed by the vulnerable tiffcrop tool (part of LibTIFF), calling processCropSelections.

When allocating memory for crop selections, input value dictates allocation size.

4. Code then writes more data than allocated (e.g., "WRITE of size 307203" or even more), overwriting adjacent heap memory.

This sort of overflow can lead to unexpected crashes or manipulation of program flow, especially in applications running with elevated privileges.

Proof-of-Concept (PoC)

Here is a pseudo-PoC for reproducing the crash using the tiffcrop utility.

# poc_tiff.py - builds a minimal TIFF with overlarge selections metainfo
from PIL import Image, TiffImagePlugin

img = Image.new("RGB", (10, 10), "white")
img.save("crafted.tiff")

# At this point you'd need to use a hex editor or bintools
# to alter the TIFF metadata "crop selections" field to a very large value,
# as the python tiff libraries don't directly write libtiff's custom fields.

print("Now edit 'crafted.tiff' and set the crop selections field to a high value.")

# Run: tiffcrop -E top cropped_input.tiff output.tiff
# Expect: Heap buffer overflow crash

Alternatively, use an available PoC such as the one linked below.

Real-World Impact

- Remote code execution: If an application automatically processes TIFF files (like a web server or photo gallery), an adversary could upload a malicious file to take control of the host.

Privilege escalation: If processed by a privileged user.

The bottom line: Never trust image files from untrusted sources.

- NIST NVD Entry
- LibTIFF Security Advisory
- oss-fuzz Report & PoC
- Upstream Patch

The fix was to enhance boundary checks and avoid trusting input fields for allocation

- crop->regionlist = _TIFFmalloc(sizeof(struct region) * crop->selections);
+ if (crop->selections > MAX_SAFE_SELECTIONS)
+     error("too many selections");
+ crop->regionlist = _TIFFmalloc(sizeof(struct region) * crop->selections);

*Upgrade to LibTIFF 4.5.1 or newer* to ensure you are protected.

Conclusion

CVE-2022-48281 is a good reminder about the dangers of trusting image metadata. Always keep libraries like LibTIFF updated, test image parsing with security in mind, and consider deploying with memory protection such as ASLR and stack canaries where possible.

Timeline

Published on: 01/23/2023 03:15:00 UTC
Last modified on: 03/02/2023 16:15:00 UTC