The Cross-Site Scripting (XSS) vulnerability is one of the most prevalent security issues in PHP web applications. To detect XSS vulnerabilities, existing dynamic techniques are commonly hindered by insufficient code exploration capabilities and non-trivial execution environment setup. Comparably, static techniques offer more flexible detection of target code by identifying vulnerable source-sink paths. However, these paths would probably be guarded by custom sanitizers (i.e., implemented to filter malicious inputs). Without establishing reliable sanitizer modeling and analysis techniques, existing work can hardly achieve satisfactory effectiveness.