ExamplePathTraversalFuzzerHooks.java

// Copyright 2021 Code Intelligence GmbH
//
// 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 com.example;

import com.code_intelligence.jazzer.api.FuzzerSecurityIssueHigh;
import com.code_intelligence.jazzer.api.HookType;
import com.code_intelligence.jazzer.api.Jazzer;
import com.code_intelligence.jazzer.api.MethodHook;
import java.lang.invoke.MethodHandle;
import java.nio.file.InvalidPathException;
import java.nio.file.Path;
import java.nio.file.Paths;

public class ExamplePathTraversalFuzzerHooks {
  private static final String publicFilesRootPath = "/app/upload/";

  @MethodHook(
      type = HookType.BEFORE,
      targetClassName = "java.io.File",
      targetMethod = "<init>",
      targetMethodDescriptor = "(Ljava/lang/String;)V")
  public static void fileConstructorHook(
      MethodHandle handle, Object thisObject, Object[] args, int hookId) {
    String path = (String) args[0];
    Path normalizedPath;
    try {
      normalizedPath = Paths.get(path).normalize();
    } catch (InvalidPathException e) {
      // Invalid paths are correctly rejected by the application.
      return;
    }
    if (!normalizedPath.startsWith(publicFilesRootPath)) {
      // Simply throwing an exception from here would not work as the calling code catches and
      // ignores all Throwables. Instead, use the Jazzer API to report a finding from a hook.
      Jazzer.reportFindingFromHook(
          new FuzzerSecurityIssueHigh(
              "Path traversal discovered: '" + path + "' --> '" + normalizedPath + "'"));
    }
  }
}