Many PHP applications run outdated versions or use vulnerable dependencies. A tool that compares code against the latest CVE database would help.
Create a CLI tool that scans installed packages and custom code for patterns matching disclosed PHP vulnerabilities. Highlight risky files with remediation advice.
Sell to agencies managing multiple client sites or enterprises with PHP monoliths. Charge per project scan or annual licenses for teams.
MVP could be a simple pattern matcher for the top 10 most critical PHP CVEs. Expand to full version analysis later.
Risk: Open-source alternatives might emerge quickly from the security community.