added better directory checking

src/main/java/io/fusionauth/http/server/HTTPContext.java

@@ -61,6 +61,9 @@ public Map<String, Object> getAttributes() {
   /**
    * Attempts to retrieve a file or classpath resource at the given path. If the path is invalid, this will return null. If the classpath is
    * borked or the path somehow cannot be converted to a URL, then this throws an exception.
+   * <p>
+   * This method protects against path traversal attacks by normalizing the resolved path and ensuring it stays within the baseDir.
+   * Attempts to escape the baseDir using sequences like {@code ../} will cause this method to return null.
    *
    * @param path The path.
    * @return The URL to the resource or null.
@@ -74,7 +77,13 @@ public URL getResource(String path) throws IllegalStateException {
     }
 
     try {
-      Path resolved = baseDir.resolve(filePath);
+      Path resolved = baseDir.resolve(filePath).normalize();
+
+      // Security: Verify the resolved path stays within baseDir to prevent path traversal attacks
+      if (!resolved.startsWith(baseDir.normalize())) {
+        return null;
+      }
+
       if (Files.exists(resolved)) {
         return resolved.toUri().toURL();
       }
@@ -98,17 +107,27 @@ public Object removeAttribute(String name) {
   }
 
   /**
-   * Locates the path given the webapps baseDir (passed into the constructor.
+   * Locates the path given the webapps baseDir (passed into the constructor).
+   * <p>
+   * This method protects against path traversal attacks by normalizing the resolved path and ensuring it stays within the baseDir.
+   * Attempts to escape the baseDir using sequences like {@code ../} will return null.
    *
    * @param appPath The app path to a resource (like an FTL file).
-   * @return The resolved path, which is almost always just the baseDir plus the appPath with a file separator in the middle.
+   * @return The resolved path, or null if the path attempts to escape the baseDir.
    */
   public Path resolve(String appPath) {
     if (appPath.startsWith("/")) {
       appPath = appPath.substring(1);
     }
 
-    return baseDir.resolve(appPath);
+    Path resolved = baseDir.resolve(appPath).normalize();
+
+    // Security: Verify the resolved path stays within baseDir to prevent path traversal attacks
+    if (!resolved.startsWith(baseDir.normalize())) {
+      return null;
+    }
+
+    return resolved;
   }
 
   /**

src/test/java/io/fusionauth/http/server/HTTPContextTest.java

@@ -0,0 +1,238 @@
+/*
+ * Copyright (c) 2026, FusionAuth, All Rights Reserved
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific
+ * language governing permissions and limitations under the License.
+ */
+package io.fusionauth.http.server;
+
+import java.io.IOException;
+import java.net.URL;
+import java.net.URLEncoder;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import org.testng.annotations.AfterMethod;
+import org.testng.annotations.BeforeMethod;
+import org.testng.annotations.Test;
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertNotNull;
+import static org.testng.Assert.assertNull;
+import static org.testng.Assert.assertTrue;
+
+/**
+ * Tests for HTTPContext focusing on path traversal security and resource resolution.
+ * <p>
+ * These tests verify that HTTPContext properly prevents path traversal attacks as described in:
+ * - CVE-2019-19781 (Citrix path traversal)
+ * - Blog post: https://blog.dochia.dev/blog/http_edge_cases/
+ *
+ * @author FusionAuth
+ */
+public class HTTPContextTest {
+  private Path tempDir;
+
+  private HTTPContext context;
+
+  @BeforeMethod
+  public void setup() throws IOException {
+    // Create a temporary directory structure for testing
+    tempDir = Files.createTempDirectory("http-context-test");
+
+    // Create legitimate test files
+    Files.writeString(tempDir.resolve("index.html"), "<html>Index</html>");
+
+    Path cssDir = Files.createDirectory(tempDir.resolve("css"));
+    Files.writeString(cssDir.resolve("style.css"), "body { color: blue; }");
+
+    Path subDir = Files.createDirectory(tempDir.resolve("subdir"));
+    Files.writeString(subDir.resolve("file.txt"), "Legitimate file");
+
+    // Create file outside the baseDir to test traversal attempts
+    Path parentDir = tempDir.getParent();
+    Files.writeString(parentDir.resolve("secret.txt"), "Secret data");
+
+    context = new HTTPContext(tempDir);
+  }
+
+  @AfterMethod
+  public void teardown() throws IOException {
+    // Cleanup temp files
+    if (tempDir != null && Files.exists(tempDir)) {
+      Files.walk(tempDir)
+           .sorted((a, b) -> b.compareTo(a)) // Delete files before directories
+           .forEach(path -> {
+             try {
+               Files.deleteIfExists(path);
+             } catch (IOException e) {
+               // Ignore cleanup errors
+             }
+           });
+    }
+
+    // Cleanup secret file from parent
+    Path secretFile = tempDir.getParent().resolve("secret.txt");
+    Files.deleteIfExists(secretFile);
+  }
+
+  /**
+   * Test that legitimate file paths work correctly.
+   */
+  @Test
+  public void testLegitimatePathsSucceed() throws Exception {
+    // Test root level file
+    URL indexUrl = context.getResource("index.html");
+    assertNotNull(indexUrl, "Should resolve index.html");
+    assertTrue(indexUrl.toString().contains("index.html"));
+
+    // Test subdirectory file
+    URL cssUrl = context.getResource("css/style.css");
+    assertNotNull(cssUrl, "Should resolve css/style.css");
+    assertTrue(cssUrl.toString().contains("style.css"));
+
+    // Test with leading slash (should be stripped)
+    URL slashUrl = context.getResource("/css/style.css");
+    assertNotNull(slashUrl, "Should resolve /css/style.css");
+    assertTrue(slashUrl.toString().contains("style.css"));
+
+    // Test nested path
+    URL subdirUrl = context.getResource("subdir/file.txt");
+    assertNotNull(subdirUrl, "Should resolve subdir/file.txt");
+    assertTrue(subdirUrl.toString().contains("file.txt"));
+  }
+
+  /**
+   * Test path traversal attack using ../ sequences (CVE-2019-19781 style).
+   * These attacks attempt to escape the baseDir and access parent directories.
+   */
+  @Test
+  public void testPathTraversalAttacksBlocked() {
+    // Simple parent directory traversal
+    URL result1 = context.getResource("../secret.txt");
+    assertNull(result1, "Should block ../secret.txt");
+
+    // Multiple parent traversals
+    URL result2 = context.getResource("../../etc/passwd");
+    assertNull(result2, "Should block ../../etc/passwd");
+
+    // Traversal with valid path prefix
+    URL result3 = context.getResource("css/../../secret.txt");
+    assertNull(result3, "Should block css/../../secret.txt");
+
+    // Deep traversal
+    URL result4 = context.getResource("subdir/../../secret.txt");
+    assertNull(result4, "Should block subdir/../../secret.txt");
+
+    // Many parent directory references
+    URL result5 = context.getResource("../../../../../../../../../etc/passwd");
+    assertNull(result5, "Should block ../../../../../../../../../etc/passwd");
+  }
+
+  /**
+   * Test URL-encoded path traversal attacks.
+   * Attackers often URL-encode the ../ sequences to bypass naive filters.
+   */
+  @Test
+  public void testUrlEncodedTraversalBlocked() {
+    // URL-encoded ../ is %2e%2e%2f
+    URL result1 = context.getResource("%2e%2e%2fsecret.txt");
+    assertNull(result1, "Should block URL-encoded traversal %2e%2e%2fsecret.txt");
+
+    URL result2 = context.getResource("%2e%2e%2f%2e%2e%2fsecret.txt");
+    assertNull(result2, "Should block %2e%2e%2f%2e%2e%2fsecret.txt");
+
+    // Mixed encoded and plain
+    URL result3 = context.getResource("css/%2e%2e%2f%2e%2e%2fsecret.txt");
+    assertNull(result3, "Should block css/%2e%2e%2f%2e%2e%2fsecret.txt");
+  }
+
+  /**
+   * Test that resolve() method also prevents path traversal.
+   */
+  @Test
+  public void testResolvePathTraversalBlocked() {
+    // Simple parent directory traversal
+    Path result1 = context.resolve("../secret.txt");
+    assertNull(result1, "Should block ../secret.txt in resolve()");
+
+    // Multiple parent traversals
+    Path result2 = context.resolve("../../etc/passwd");
+    assertNull(result2, "Should block ../../etc/passwd in resolve()");
+
+    // Traversal with valid path prefix
+    Path result3 = context.resolve("css/../../secret.txt");
+    assertNull(result3, "Should block css/../../secret.txt in resolve()");
+  }
+
+  /**
+   * Test that resolve() works correctly for legitimate paths.
+   */
+  @Test
+  public void testResolveLegitimatePathsSucceed() {
+    // Test root level file
+    Path indexPath = context.resolve("index.html");
+    assertNotNull(indexPath, "Should resolve index.html");
+    assertEquals(indexPath, tempDir.resolve("index.html"));
+
+    // Test subdirectory file
+    Path cssPath = context.resolve("css/style.css");
+    assertNotNull(cssPath, "Should resolve css/style.css");
+    assertEquals(cssPath, tempDir.resolve("css/style.css"));
+
+    // Test with leading slash
+    Path slashPath = context.resolve("/css/style.css");
+    assertNotNull(slashPath, "Should resolve /css/style.css");
+    assertEquals(slashPath, tempDir.resolve("css/style.css"));
+  }
+
+  /**
+   * Test edge case: path that goes down then up but stays within baseDir.
+   * For example: "subdir/../index.html" should resolve to "index.html"
+   */
+  @Test
+  public void testNormalizedPathWithinBaseDirSucceeds() {
+    // This path traverses up but stays within baseDir after normalization
+    URL result = context.getResource("subdir/../index.html");
+    assertNotNull(result, "Should allow subdir/../index.html as it normalizes to index.html");
+    assertTrue(result.toString().contains("index.html"));
+
+    Path resolved = context.resolve("subdir/../index.html");
+    assertNotNull(resolved, "Should resolve subdir/../index.html");
+    assertEquals(resolved, tempDir.resolve("index.html"));
+  }
+
+  /**
+   * Test that non-existent files return null (not exceptions).
+   */
+  @Test
+  public void testNonExistentFileReturnsNull() {
+    URL result = context.getResource("does-not-exist.txt");
+    assertNull(result);
+  }
+
+  /**
+   * Test attribute storage (not security related, but completeness).
+   */
+  @Test
+  public void testAttributeStorage() {
+    context.setAttribute("test", "value");
+    assertEquals(context.getAttribute("test"), "value");
+
+    context.setAttribute("number", 42);
+    assertEquals(context.getAttribute("number"), 42);
+
+    Object removed = context.removeAttribute("test");
+    assertEquals(removed, "value");
+    assertNull(context.getAttribute("test"));
+  }
+}