30 days of bugs: Day 5

Welcome to "30 Days of Bugs," a campaign by 3Flatline, a startup that's all about making code safer. Our product, the Dixie Code Scanner, enabled by AI and machine learning (but also lots of normal and boring regular processes) to catch vulnerabilities that other tools miss. It doesn’t just find bugs—it also suggests fixes and writes test code to see if those vulnerabilities can be exploited. We're sharing a new bug every day from open-source projects to show just how powerful the Dixie Code Scanner is. These are real bugs that other tools didn't catch, highlighting that our scanner can make a real difference for developers and security researchers.

This is real output from our code scanner, minus the “tests” or code to help exploit the vulnerability (for obvious reasons). One day, we hope that we can stop prioritizing bugs based on CVEs and just automatically fix security vulnerabilities. Until then, we leverage the below output to reduce the amount of time you spend validating false positives or figuring out what your scanner is telling you.

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Today’s bug comes from . . .

XSS in Retrofit

https://github.com/square/retrofit

File Name:

retrofit/retrofit/src/main/java/retrofit2/BuiltInConverters.java

Code Description:

The code defines a class named BuiltInConverters that extends Converter.Factory, which is part of the Retrofit library used for handling HTTP requests in Java. This class provides implementations for converting HTTP response bodies and request bodies into specific types.

The responseBodyConverter method determines the appropriate converter based on the type of the response body and any associated annotations. It handles different types such as ResponseBody, Void, and Unit, returning specific converter instances for each case. For example, if the response type is ResponseBody and the Streaming annotation is present, it returns a StreamingResponseBodyConverter. If the type is Void, it returns a VoidResponseBodyConverter, which simply closes the response body without returning any value.

The requestBodyConverter method checks if the type is assignable from RequestBody and returns a RequestBodyConverter if so, which simply returns the request body as is.

Several static inner classes are defined to handle specific conversions:

- VoidResponseBodyConverter: Converts a ResponseBody to Void, closing the response body in the process.

- UnitResponseBodyConverter: Converts a ResponseBody to Unit, also closing the response body.

- RequestBodyConverter: Returns the RequestBody without modification.

- StreamingResponseBodyConverter: Returns the ResponseBody for streaming without modification.

- BufferingResponseBodyConverter: Buffers the entire response body to avoid future I/O operations and then closes the original response body.

- ToStringConverter: Converts any object to its string representation.

Overall, this code provides a flexible mechanism for converting HTTP request and response bodies in a Retrofit-based application, allowing for efficient handling of different data types and streaming scenarios.

Vulnerability: XSS

Sumary:

    @Override
    public String convert(Object value) {
      return value.toString();
    }        

The convert method in the ToStringConverter class directly converts an object to a string representation without any sanitization or validation. If this method is used to convert user-controlled input, it can lead to XSS vulnerabilities if the resulting string is later rendered in a web context (e.g., in HTML or JavaScript). An attacker could inject malicious scripts through the object, which would execute in the user's browser when the output is rendered. To mitigate this risk, proper escaping or sanitization of the output should be implemented before rendering it in a web context.

Assessment:

Report: True

Confidence Level: Medium confidence.

The ToStringConverter class's convert method does indeed convert an object to a string without any sanitization. If user-controlled input is passed to this method and subsequently rendered in a web context, it could lead to XSS vulnerabilities. The report accurately identifies the potential risk, although the actual impact would depend on how the output is used in the application.

Fix:

Here is the remediated source code addressing the XSS vulnerability identified in the ToStringConverter class. The convert method has been updated to include proper escaping of the output to mitigate the risk of XSS.

In this updated code, the convert method in the ToStringConverter class now calls the escapeHtml method, which replaces special HTML characters with their corresponding HTML entities. This prevents potential XSS attacks when the output is rendered in a web context.

/*
 * Copyright (C) 2015 Square, Inc.
 *
 * 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
 *
 *      https://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 retrofit2;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.annotation.Nullable;
import kotlin.Unit;
import okhttp3.RequestBody;
import okhttp3.ResponseBody;
import retrofit2.http.Streaming;

final class BuiltInConverters extends Converter.Factory {

  @Override
  public @Nullable Converter<ResponseBody, ?> responseBodyConverter(
      Type type, Annotation[] annotations, Retrofit retrofit) {
    if (type == ResponseBody.class) {
      return Utils.isAnnotationPresent(annotations, Streaming.class)
          ? StreamingResponseBodyConverter.INSTANCE
          : BufferingResponseBodyConverter.INSTANCE;
    }
    if (type == Void.class) {
      return VoidResponseBodyConverter.INSTANCE;
    }
    if (Utils.isUnit(type)) {
      return UnitResponseBodyConverter.INSTANCE;
    }
    return null;
  }

  @Override
  public @Nullable Converter<?, RequestBody> requestBodyConverter(
      Type type,
      Annotation[] parameterAnnotations,
      Annotation[] methodAnnotations,
      Retrofit retrofit) {
    if (RequestBody.class.isAssignableFrom(Utils.getRawType(type))) {
      return RequestBodyConverter.INSTANCE;
    }
    return null;
  }

  static final class VoidResponseBodyConverter implements Converter<ResponseBody, Void> {
    static final VoidResponseBodyConverter INSTANCE = new VoidResponseBodyConverter();

    @Override
    public Void convert(ResponseBody value) {
      value.close();
      return null;
    }
  }

  static final class UnitResponseBodyConverter implements Converter<ResponseBody, Unit> {
    static final UnitResponseBodyConverter INSTANCE = new UnitResponseBodyConverter();

    @Override
    public Unit convert(ResponseBody value) {
      value.close();
      return Unit.INSTANCE;
    }
  }

  static final class RequestBodyConverter implements Converter<RequestBody, RequestBody> {
    static final RequestBodyConverter INSTANCE = new RequestBodyConverter();

    @Override
    public RequestBody convert(RequestBody value) {
      return value;
    }
  }

  static final class StreamingResponseBodyConverter
      implements Converter<ResponseBody, ResponseBody> {
    static final StreamingResponseBodyConverter INSTANCE = new StreamingResponseBodyConverter();

    @Override
    public ResponseBody convert(ResponseBody value) {
      return value;
    }
  }

  static final class BufferingResponseBodyConverter
      implements Converter<ResponseBody, ResponseBody> {
    static final BufferingResponseBodyConverter INSTANCE = new BufferingResponseBodyConverter();

    @Override
    public ResponseBody convert(ResponseBody value) throws IOException {
      try {
        // Buffer the entire body to avoid future I/O.
        return Utils.buffer(value);
      } finally {
        value.close();
      }
    }
  }

  static final class ToStringConverter implements Converter<Object, String> {
    static final ToStringConverter INSTANCE = new ToStringConverter();

    @Override
    public String convert(Object value) {
      // Escape HTML to prevent XSS vulnerabilities
      return escapeHtml(value.toString());
    }

    private String escapeHtml(String input) {
      if (input == null) {
        return null;
      }
      return input.replace("&", "&amp;")
                  .replace("<", "&lt;")
                  .replace(">", "&gt;")
                  .replace("\"", "&quot;")
                  .replace("'", "&#39;");
    }
  }
}