CVE-2021-45911

What it actually does

Heap-based buffer overflow in the main function allows writing two bytes beyond allocated buffer boundaries, enabling memory corruption that can lead to arbitrary code execution or application crash.

Why it matters to the business

Attackers can gain control of systems that process untrusted GIF files with this converter, potentially leading to data theft, ransomware deployment, or full system compromise in environments relying on this tool for image processing workflows.

How an attack unfolds

An attacker crafts a malicious GIF file that triggers the heap overflow during conversion; the victim runs gif2apng on the file locally, allowing the overflow to corrupt memory and execute attacker-controlled code without needing elevated privileges beyond normal user context.

How to fix it

Discontinue use of gif2apng 1.9 and replace with a maintained alternative image converter; if source is available, rebuild after applying upstream patches that correct the buffer handling in the main function; enforce strict input validation and sandboxing for any remaining image processing tools.

How to confirm the fix worked

Test the updated or replacement converter against known trigger GIF samples in a controlled environment to confirm no buffer overrun occurs; scan source repositories and package inventories for presence of gif2apng 1.9 binaries or scripts.

Typical attack path

1. Craft malicious GIF input designed to overflow the heap buffer by two bytes
2. Deliver the file to the target via email, web download, or shared storage
3. Victim executes gif2apng against the file with normal user privileges
4. Overflow corrupts adjacent heap memory enabling code execution or crash
5. Attacker payload establishes persistence or exfiltrates data

How to detect it

Review command-line history, process execution logs, and file access records on endpoints for invocations of gif2apng against external or untrusted GIF inputs; correlate with subsequent unexpected process spawns or memory corruption crashes in system logs.

What your security team should do

• Immediately inventory all systems for gif2apng usage and remove or replace version 1.9
• Block execution of untrusted image conversion utilities via application allowlisting
• Monitor for new releases or community forks that address the buffer handling defect
• Educate users on risks of running third-party converters on unverified files