Vulnerability scanners test web applications for known and unknown security issues through crawling, error analysis, and testing techniques like SQL injection and XSS. When security devices like WAF/IPS are deployed between scanners and servers, interpretation becomes complex.
Negative scan results don’t conclusively prove security – they might indicate blocked attacks rather than absent vulnerabilities. Key challenges include:
- Unable to confirm if vulnerabilities exist or were simply blocked in transit
- Cannot differentiate between real flaws and generic attack scripts
- Stateful attacks requiring session continuity are difficult to simulate
- False positives/negatives remain unquantifiable
The conclusion: “from the subset of attack vectors that the vulnerability scanner has, some or all of this signatures have been mitigated - by the IPS/WAF, or somehow by the application.”
We need improved tools that understand backend systems, can send legitimate traffic to verify proper responses, and potentially include server-side agents confirming actual attack reach.