CVE-2016-10166

What it actually does

Integer underflow in _gdContributionsAlloc in gd_interpolation.c allows remote attackers to trigger memory corruption via crafted image data that decrements the u variable below zero.

Why it matters to the business

Enables remote compromise of systems that process user-supplied images through libgd, risking data exposure, service outages, or full system takeover in web servers and applications across many Linux distributions.

How an attack unfolds

An attacker supplies a malicious image to any application linked against a vulnerable libgd build; the image triggers the integer underflow during interpolation, corrupting heap memory that an attacker can then leverage for arbitrary code execution.

How to fix it

Upgrade libgd to 2.2.4 or newer. Apply the exact package updates listed for each distribution: Debian 11/12/13 to 4.9.30-1; Ubuntu 14.04 LTS kernels to 3.13.0-129.178 or 4.4.0-83.106~14.04.1 variants; Ubuntu 16.04 LTS kernels to 4.4.0-83.106, 4.4.0-1022.31, 4.11.0-1009.9, 4.10.0-33.37~16.04.1, 4.13.0-1008.9, 4.4.0-1061.69 or 4.4.0-1063.68 as applicable.

How to confirm the fix worked

Confirm installed libgd version reports 2.2.4 or later; verify package manager output matches the fixed versions for the running distribution and kernel; re-test image-processing code paths with known-good inputs.

Typical attack path

1. Deliver crafted image file to a network service that invokes libgd image functions
2. Trigger _gdContributionsAlloc with input that causes u to underflow
3. Achieve memory corruption leading to control-flow hijacking or data leakage

How to detect it

Review web-server and application logs for crashes or segmentation faults during image handling; monitor process memory usage anomalies around libgd-linked binaries; search historic logs for unexpected terminations of services that call gd interpolation routines.

What your security team should do

• Immediately apply the distribution-specific package updates listed in remediation guidance
• Inventory all systems using libgd and prioritize those reachable from untrusted image sources
• Disable image-processing features that rely on libgd until patches are deployed where feasible