CVE-2025-46393 - Severe Packet Size Mishandling in ImageMagick’s Multispectral MIFF Image Processing (Pre-7.1.1-44)
CVE-2025-46393 is a critical security vulnerability affecting ImageMagick (versions before 7.1.1-44), an open-source image processing toolkit popular with web apps and image editing tools. The vulnerability exists due to mishandling of the packet_size during the processing of MIFF images containing multispectral data. This mismanagement, particularly when rendering all image channels in arbitrary order, can lead to heap buffer overflows and allows attackers to potentially execute malicious code remotely.
In this post, I’ll break down the vulnerability in clear terms, show relevant code snippets, walk through how the exploit works, and link to trusted sources for those wanting to read more or patch systems.
What is MIFF in ImageMagick?
MIFF (Magick Image File Format) is a flexible format used internally by ImageMagick supporting multiple channels and depths—sometimes for advanced tasks, like multispectral imagery.
When loading a MIFF file, ImageMagick parses channel data for each pixel. For multispectral images, pixels may contain more than just the usual RGBA (e.g., infrared, ultraviolet). Handling this extra data can be tricky, especially when channels are processed in an unpredictable (i.e., user-defined or file-supplied) order.
Where Does It Go Wrong?
The heart of this vulnerability is how packet sizes—the amount of memory allocated/used to store pixel channel data per row—are calculated and validated. When ImageMagick is asked to process channels non-sequentially or in an arbitrary order, the code that sets up packet_size can become inconsistent with the actual number of bytes being written to memory.
Consider this illustrative code fragment (simplified for clarity)
// Vulnerable ImageMagick code (pre-7.1.1-44)
size_t packet_size = number_of_channels * QuantumDepth / 8;
for (size_t i = ; i < rows; i++) {
unsigned char *pixels = buffer + i * packet_size;
for (size_t j = ; j < number_of_channels; j++) {
// Populates each channel's data
pixels[ /* channel offset */ ] = ...;
}
}
The problem? If a MIFF file declares an arbitrary channel order with unexpected values—or even repeats or omits channels—the calculated packet_size will not match the actual data processed and written. That lets an attacker overrun the buffer or read out-of-bounds, risking a heap buffer overflow. In some scenarios, an attacker can craft a MIFF file to write shellcode into memory and hijack execution.
Exploit Scenario
Suppose an attacker uploads a malicious MIFF file via a web application (maybe a profile picture or document preview system using ImageMagick under the hood). They *carefully* structure channel order metadata so that ImageMagick’s computation allocates a smaller buffer than required.
Data ends up in memory it doesn’t own.
- This can corrupt heap structures, sometimes making it possible for an attacker to control program flow (for example, via a ROP chain, classic heap overflow stuff).
A proof-of-concept (PoC) vulnerable MIFF snippet might look like
id=ImageMagick
columns=1
rows=1
channel-type=Intensity,Alpha,Intensity,CMYK # Intentional duplicate & wrong order!
...
binary pixel data here with crafted excess bytes
(For ethical reasons, I omit a working exploit file, but you get the idea.)
ImageMagick Security Advisory:
https://github.com/ImageMagick/Website/security/advisories/GHSA-l1z5-fx2g-5m2p
CVE Details:
https://nvd.nist.gov/vuln/detail/CVE-2025-46393
Upstream Patch Discussion:
https://github.com/ImageMagick/ImageMagick/commit/19d6cfcf8d77d7467df5f579b3a5bb620e8289b
ImageMagick Official Site:
Upgrade Now:
Update to ImageMagick version 7.1.1-44 or newer immediately, especially if your apps accept user-uploaded images.
Sanitize Inputs:
Filter uploaded images if possible. Consider rejecting or converting unusual file types before sending them to ImageMagick.
Isolate ImageMagick:
Run image processing as a low-privilege user or even in a sandbox/container.
Summary
*CVE-2025-46393* is a high-impact vulnerability, illustrating how minor math errors in image parsing can let attackers hijack an entire system. If your stack uses ImageMagick—even via libraries or plugins—act now to avoid being caught by a malicious MIFF file.
Please consult the official advisory for ongoing information. Stay safe and patch early!
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Timeline
Published on: 04/23/2025 15:16:01 UTC