CVE-2022-3095: Critical Dart and Flutter URI Parsing Vulnerability Leads to Potential Auth Bypass in Web Applications

A recently discovered vulnerability, identified as CVE-2022-3095, affects the Dart URI class implementation for versions prior to 2.18 and Flutter versions prior to 3.30. This vulnerability lies in the backslash parsing incompatibilities with the '\' character in URIs, which can potentially lead to auth bypass in web applications interpreting URIs. In this post, we will dive into the details of CVE-2022-3095, including how it arises, how it can be exploited, and the necessary steps to mitigate the issue.

Understanding the Vulnerability

CVE-2022-3095 arises due to a deviation from the WhatWG URL standards in the Dart URI class implementation. Dart follows the RFC 3986 syntax for URIs, which creates incompatibilities with the '\' characters when parsing URIs. This can lead to incorrect parsing and unexpected behavior in web applications developed using Dart or Flutter.

For instance, consider a web application developed using Dart or an older version of Flutter that validates users based on their email addresses. An attacker might be able to bypass the email validation procedure by using backslashes in their email addresses. Let's take a look at a sample Dart code snippet to illustrate this point.

Original Code Snippet:

import 'dart:core';

void main() {
  String emailAddress = r'user\@example.com';
  Uri myUri = Uri.parse(emailAddress);

  if (emailAddress.contains('@')) {
    print("Valid email address!");
  } else {
    print("Invalid email address!");
  }
}

The above code snippet is expected to check if the provided email address is valid by searching for the '@' symbol, which is a required component of a valid email address. However, due to the backslash incompatibilities, this code may misinterpret the attacker's email address, leading to an auth bypass.

Exploit Details

To exploit this vulnerability, an attacker can craftily manipulate the '\' character in the URI components. For instance, they can try inserting the '\' character before the '@' symbol in an email address to deceive the email validation process. The following modified code snippet demonstrates this exploit.

Modified Code Snippet (Exploit):

import 'dart:core';

void main() {
  String emailAddress = r'user\\@example.com';
  Uri myUri = Uri.parse(emailAddress);

  if (emailAddress.contains('@')) {
    print("Valid email address!");
  } else {
    print("Invalid email address!");
  glEnd
}

In the modified code snippet, the attacker has added an extra backslash before the '@' symbol in the email address. Since the Dart URI implementation does not correctly handle these backslashes, the email validation logic in the web application will be bypassed, and the attacker will now be considered a valid user, despite providing an invalid email address.

Mitigation

To mitigate this vulnerability, it is highly recommended to update the affected versions of Dart and Flutter.

* For Dart users: Update to Dart version 2.18 or later. Find more information about the latest Dart version and updating instructions in the official Dart documentation.
* For Flutter users: Update to Flutter version 3.30 or later. You can find detailed information on updating your Flutter version in the official Flutter documentation.

Additionally, developers must always validate and sanitize user input, especially shared components like email addresses, to prevent potential security vulnerabilities.

Conclusion

CVE-2022-3095 is a critical vulnerability that affects the Dart and Flutter URI parsing implementation. It highlights the importance of thoroughly validating and sanitizing user input in web applications. By updating Dart and Flutter to their latest versions and following best practices in web development, developers can mitigate the CVE-2022-3095 vulnerability and build more secure applications.

Timeline

Published on: 10/27/2022 16:15:00 UTC
Last modified on: 10/31/2022 16:20:00 UTC