CVE-2013-7456

What it actually does

Out-of-bounds read in gd_interpolation.c imagescale implementation triggers memory corruption, enabling denial of service or unspecified further impact when processing a malicious image.

Why it matters to the business

Applications that resize user-supplied images may crash or behave unexpectedly, causing service outages, support overhead, and potential exposure of sensitive memory contents to remote attackers.

How an attack unfolds

An attacker crafts a specially malformed image that triggers the flawed interpolation path, then causes a vulnerable PHP application to call imagescale on the image, resulting in an out-of-bounds read that can crash the process or allow further manipulation.

How to fix it

Upgrade libgd to version 2.1.1 or later and PHP to 5.5.36 or later, 5.6.22 or later, or 7.0.7 or later. Disable image scaling of untrusted input until patches are applied.

How to confirm the fix worked

Verify installed libgd and PHP versions against the fixed releases, then test image processing endpoints with known-good and boundary images to confirm absence of crashes or abnormal behavior.

Typical attack path

1. Locate a PHP application that accepts and resizes images using the imagescale function
2. Prepare a crafted image file designed to exercise the vulnerable code path in libgd
3. Submit the image to the application via upload, URL fetch, or API endpoint
4. Trigger the imagescale call and observe denial of service or memory disclosure

How to detect it

Review web server and PHP error logs for segmentation faults or out-of-bounds access messages during image processing; correlate spikes in image upload activity with process restarts or memory errors.

What your security team should do

• Prioritize patching PHP and libgd installations that handle user-provided images
• Implement input validation and size limits on all image upload paths
• Monitor application logs and process health for image-processing crashes
• Consider sandboxing or isolating image manipulation workloads