CVE-2017-6362

What it actually does

Double free in gdImagePngPtr when processing a PNG palette containing zero colors, resulting in memory corruption that crashes the process.

Why it matters to the business

Applications relying on libgd for image handling can be crashed remotely, causing denial of service and potential downtime for image-dependent services.

How an attack unfolds

An attacker crafts a minimal PNG with an empty color palette and supplies it to any application that calls gdImagePngPtr; the double-free triggers on the second free of the same palette structure, crashing the process.

How to fix it

Upgrade libgd to the commit 8255231b68889597d04d451a72438ab92a405aba or later release containing the fix; rebuild and redeploy all dependent applications.

How to confirm the fix worked

Confirm the installed libgd version or commit hash is at or beyond 8255231b68889597d04d451a72438ab92a405aba; re-test the service with a zero-color-palette PNG to verify it no longer crashes.

Typical attack path

1. Identify a network endpoint or file upload that invokes libgd PNG encoding
2. Generate a PNG containing a zero-color palette
3. Deliver the image to the target function via HTTP, file upload, or API
4. Trigger gdImagePngPtr to cause the double free and crash

How to detect it

Review application and system logs for repeated crashes or segmentation faults during PNG encoding; correlate with inbound image uploads or API calls that process user-supplied PNG data.

What your security team should do

• Immediately update all instances of libgd to the fixed commit
• Scan internal codebases and containers for older libgd versions
• Add the fixed version to dependency pinning and CI build checks
• Monitor crash logs for segmentation faults during PNG processing until patches are deployed