🛡️ Sentinel: [CRITICAL] 심볼릭 링크를 통한 경로 탐색 취약점 수정

.jules/sentinel.md

@@ -22,3 +22,8 @@
 **Vulnerability:** Defense in Depth (CSP Missing)
 **Learning:** Even when inputs are properly escaped, statically generated HTML that displays file/directory structures should implement a Content Security Policy (CSP) to provide an extra layer of defense against potential XSS bypasses.
 **Prevention:** Include a strict CSP meta tag (e.g., `default-src 'none'; style-src 'unsafe-inline';`) in auto-generated HTML headers when external scripts or resources are not required.
+
+## 2024-07-04 - Path Traversal bypass via canonicalFile
+**Vulnerability:** Bypass of `NOFOLLOW_LINKS` check for symbolic links during directory crawling top level check.
+**Learning:** Using `File.canonicalFile` resolves symbolic links before any subsequent checks. If you then call `Files.isDirectory(path, LinkOption.NOFOLLOW_LINKS)` on the canonicalized file, the symlink has already been followed and resolved to its target, meaning the `NOFOLLOW_LINKS` option fails to detect that it was originally a symlink.
+**Prevention:** Use `File.absoluteFile` instead of `File.canonicalFile` when preparing files for symlink validation checks so that the original symlink is preserved and correctly rejected by `NOFOLLOW_LINKS`.

src/main/kotlin/html4tree/main.kt

@@ -23,7 +23,10 @@ fun main(args: Array<String>)  = Html4tree().main(args)
 
 fun go(topDir: String, maxLevel: Int)  {
     require(topDir.isNotBlank())
-    val top_dir = File(topDir).canonicalFile
+    // SECURITY: Use absoluteFile instead of canonicalFile to avoid prematurely
+    // resolving symlinks, which would bypass the NOFOLLOW_LINKS check below
+    // and potentially allow path traversal vulnerabilities via symlinks.
+    val top_dir = File(topDir).absoluteFile
     require(Files.isDirectory(top_dir.toPath(), LinkOption.NOFOLLOW_LINKS)) { "Top directory must be an existing non-symlink directory" }
 
     val ll = LinkedList()