Cross-Site Scripting in Java

Hoch CWE-79 Draft — pending review

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Einfach erklärt

Imagine a bulletin board where someone posts an instruction that forces the viewer's computer to secretly send their session cookie to an attacker.

output encoding: Converting special markup characters into safe entities so browsers display them as text rather than script.

Was passiert

XSS in Java web applications occurs when JSP, Thymeleaf, or FreeMarker templates render request parameters directly into response streams without encoding.

Auswirkung in der Praxis

In 2005, the Samy XSS worm infected over 1 million user profiles on MySpace in under 20 hours, forcing the platform offline.

Documented historical AppSec case study.

Verwundbar vs. behoben

VULNERABLE



  Welcome, <%= request.getParameter("name") %>

FIXED



  Welcome,

Warum die Behebung funktioniert

JSTL and Thymeleaf th:text convert sensitive HTML characters (<, >, &, ") into inert HTML entities.

Sprachspezifische Gotchas

Thymeleaf th:utext

th:utext explicitly disables escaping. Use th:text for untrusted data.

Häufige Missverständnisse

"Spring Boot automatically prevents all XSS"

Spring handles URL and JSON encoding, but template rendering depends on proper tag usage.

Wie Sie prüfen, ob Sie betroffen sind

grep -rn "<%=.*getParameter" --include="*.jsp" . grep -rn "th:utext" --include="*.html" .

Scan JSP and template views using FindSecBugs (rule XSS_REQUEST_PARAMETER_TO_JSP_WRITER).

Präventions-Checkliste

✓Use in JSP or th:text in Thymeleaf
✓Run FindSecBugs in CI to catch unescaped output

Häufig gestellte Fragen

How should rich user HTML be handled in Java?

Use OWASP Java HTML Sanitizer to strip dangerous tags and attributes before rendering.

Referenzen

Ansehen in: Java Python JavaScript Java Go PHP C# Rust

Siehe auch: SQL Injection Command InjectionPath Traversal