クロスサイトスクリプティング in Java

重要 CWE-79 Draft — pending review

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かんたん解説 (ELI5)

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.

何が起きているか

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

実際の被害事例

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.

脆弱なコード vs 安全なコード

VULNERABLE



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

FIXED



  Welcome,

なぜ対策コードで防げるのか

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

言語固有の落とし穴

Thymeleaf th:utext

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

よくある誤解

"Spring Boot automatically prevents all XSS"

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

影響の有無を確認する方法

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).

防止チェックリスト

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

よくある質問 (FAQ)

How should rich user HTML be handled in Java?

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

参考資料

表示言語: Java Python JavaScript Java Go PHP C# Rust

関連する脆弱性: SQL Injection Command InjectionPath Traversal