PHP filter_var shenanigans
It is likely that we have all seen PHP filters that prevent us from encountering vulnerabilities. Here in this blog post, I’ll walk you through my thought process for bypassing a filter by looking for a bug in the filter itself in order to reach a bug! Let’s pretend we have the following code, which passes some user-input to filter_var() and uses the FILTER_VALIDATE_DOMAIN or FILTER FLAG HOSTNAME flag. This adds the functionality to validate hostnames on a per-host rationale ...
Source: pwning.systems