CVE-2020-27818

What it actually does

Memory corruption in the check_chunk_name function allows a malformed PNG chunk name to trigger a crash or temporary hang during file parsing.

Why it matters to the business

Attackers can briefly interrupt pngcheck processing on user workstations or build pipelines, causing short availability loss with minimal overall operational effect.

How an attack unfolds

An attacker crafts a PNG containing an invalid chunk name, then supplies the file to pngcheck via command line or automated scanning; the tool crashes or stalls until restarted.

How to fix it

Upgrade pngcheck to a version newer than 2.4.0 that resolves the chunk-name validation issue; rebuild any dependent packages in Fedora or Debian distributions once corrected packages are released.

How to confirm the fix worked

Confirm pngcheck version is greater than 2.4.0 and test with known-malformed test files to verify the process no longer crashes.

Typical attack path

1. Craft a PNG file with a malformed chunk name that triggers the flaw in check_chunk_name
2. Deliver the file to a target system where pngcheck is executed
3. Invoke pngcheck against the malicious file, causing the process to terminate or hang
4. Repeat as needed to sustain temporary denial of service

How to detect it

Review process crash logs and command-line history for pngcheck invocations on files that produce segmentation faults or unexpected exits; correlate with file creation timestamps.

What your security team should do

• Prioritize updating pngcheck across developer workstations and CI pipelines
• Disable pngcheck execution on untrusted files until patched
• Monitor upstream libpng and distribution repositories for corrected packages