diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 6c61284..215421a 100644
--- a/.jules/sentinel.md
+++ b/.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.
+
+## 2024-11-20 - [html4tree] Symlink Path Traversal Bypass via canonicalFile
+**Vulnerability:** Symlink paths bypassed directory symlink checks causing path traversal vulnerabilities at the root directory level.
+**Learning:** `File.canonicalFile` resolves symbolic links immediately. When used *before* security checks like `Files.isDirectory(..., LinkOption.NOFOLLOW_LINKS)`, the check evaluates the resolved target rather than the symlink itself, defeating the entire purpose of `NOFOLLOW_LINKS`.
+**Prevention:** Use `File.absoluteFile` instead of `File.canonicalFile` when handling paths that require subsequent non-following symlink checks (e.g., using `LinkOption.NOFOLLOW_LINKS`), ensuring the symlink itself is checked before any resolution occurs.
diff --git a/src/main/kotlin/html4tree/main.kt b/src/main/kotlin/html4tree/main.kt
index 2e2809f..d827644 100644
--- a/src/main/kotlin/html4tree/main.kt
+++ b/src/main/kotlin/html4tree/main.kt
@@ -23,12 +23,12 @@ fun main(args: Array<String>)  = Html4tree().main(args)
 
 fun go(topDir: String, maxLevel: Int)  {
     require(topDir.isNotBlank())
-    val top_dir = File(topDir).canonicalFile
-    require(Files.isDirectory(top_dir.toPath(), LinkOption.NOFOLLOW_LINKS)) { "Top directory must be an existing non-symlink directory" }
+    val topDirFile = File(topDir).absoluteFile
+    require(Files.isDirectory(topDirFile.toPath(), LinkOption.NOFOLLOW_LINKS)) { "Top directory must be an existing non-symlink directory" }
 
     val ll = LinkedList()
 
-    ll.push(LinkedListEntry(top_dir,0))
+    ll.push(LinkedListEntry(topDirFile,0))
 
     var lle: LinkedListEntry? = ll.pull()