🛡️ Sentinel: [MEDIUM] Fix DoS and resource exhaustion in ignore file processing

.jules/sentinel.md

@@ -22,3 +22,7 @@
 **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.
+## 2024-07-02 - Malicious ignore files cause DoS
+**Vulnerability:** A malicious actor could place a directory named `.html4ignore` or a massive `.html4ignore` file, leading to application crashes (`java.io.FileNotFoundException: .html4ignore (Is a directory)`) or memory/resource exhaustion.
+**Learning:** Applications reading hidden configuration files from user-controlled directories must validate file type (isFile) and size before loading them into memory.
+**Prevention:** Add checks for `isFile` and enforce a reasonable file size limit (e.g., 1MB) before parsing directory-level configuration files.

src/main/kotlin/html4tree/main.kt

@@ -23,7 +23,7 @@ fun main(args: Array<String>)  = Html4tree().main(args)
 
 fun go(topDir: String, maxLevel: Int)  {
     require(topDir.isNotBlank())
-    val top_dir = File(topDir).canonicalFile
+    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()
@@ -88,7 +88,7 @@ fun process_ignore_file(curr_dir: File): Set<String> {
 
     val files_to_exclude = mutableSetOf<String>()
 
-    if(ignore_file.exists()){
+    if(ignore_file.exists() && ignore_file.isFile() && ignore_file.length() <= 1048576){ // Limit to 1MB
        val ignored_regexes = mutableListOf<Regex>()
 
        ignore_file.forEachLine {

src/test/kotlin/html4tree/SentinelTest.kt

@@ -0,0 +1,47 @@
+package html4tree
+
+import org.junit.Test
+import java.io.File
+import java.nio.file.Files
+import kotlin.test.assertTrue
+import kotlin.test.assertFalse
+
+class SentinelTest {
+
+    @Test
+    fun testIgnoreFileIsDirectory() {
+        val tempDir = Files.createTempDirectory("html4tree-test-sentinel").toFile()
+        try {
+            val ignoreDir = File(tempDir, ".html4ignore")
+            ignoreDir.mkdir() // Create a directory instead of a file
+
+            val testFile = File(tempDir, "test.txt")
+            testFile.createNewFile()
+
+            // Should not crash, and test.txt shouldn't be excluded
+            val excluded = process_ignore_file(tempDir)
+            assertFalse(excluded.contains("test.txt"))
+        } finally {
+            tempDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun testIgnoreFileIsTooLarge() {
+        val tempDir = Files.createTempDirectory("html4tree-test-sentinel").toFile()
+        try {
+            val ignoreFile = File(tempDir, ".html4ignore")
+            val chars = ByteArray(1024 * 1024 + 10) { 'a'.toByte() }
+            ignoreFile.writeBytes(chars) // Create file slightly larger than 1MB
+
+            val testFile = File(tempDir, "test.txt")
+            testFile.createNewFile()
+
+            // Should not crash, and test.txt shouldn't be excluded since the file is ignored
+            val excluded = process_ignore_file(tempDir)
+            assertFalse(excluded.contains("test.txt"))
+        } finally {
+            tempDir.deleteRecursively()
+        }
+    }
+}