A vulnerability CVE-2022-48565, an XML External Entity (XXE) issue, was recently discovered in Python up to version 3.9.1. This issue potentially exposes the application to security risks, and in response, the plistlib module no longer accepts entity declarations in XML plist files. This post will provide an in-depth look at the exploit, how it affects the plistlib module, and how to mitigate the problem, with direct references to credible sources and code snippets for easy understanding.

Background on XXE

XML External Entity (XXE) vulnerabilities happen when an application parses XML input that includes a reference to an external entity. This external entity may contain sensitive data or can be used to launch attacks against the machine or application. For more information on XXE vulnerabilities and prevention, you can refer to the OWASP XXE Cheat Sheet [1].

Affected Versions

This vulnerability affects Python up to version 3.9.1. If you are using an earlier version of Python, it is highly recommended that you update to a more recent and secure version.

Exploit Details

In this case, the vulnerability lies within Python's plistlib module, which is responsible for handling Apple property list files. The plistlib module parses plist files as XML, and prior to version 3.9.2, it did not properly sanitize entity declarations in the XML, making it vulnerable to XXE attacks. An attacker can craft a malicious XML plist file that takes advantage of this vulnerability and potentially gain unauthorized access to sensitive data or perform a denial of service (DoS) attack by consuming system resources.

Mitigation Steps

To mitigate this issue, Python developers have removed the acceptance of entity declarations in XML plist files in the plistlib module starting from version 3.9.2. Upgrading your Python installation to a safe version (3.9.2 or higher) will protect your application from this vulnerability.

Here is a code snippet showcasing the change in the plistlib module in Python 3.9.2

# In Python 3.9.2, the plistlib module has been modified to disable entity declarations in XML plist files
def load(fp, *, fmt=None, use_builtin_types=True, dict_type=dict):
    if fmt is None:
        fmt = _FORMAT_BINARY if fp.read(6) == b'bplist' else _FORMAT_XML
        fp.seek()

    if fmt == _FORMAT_XML:
        # Starting from Python 3.9.2, passing huge_tree=False and resolve_entities=False to xml.etree.ElementTree.parse
        return readPlistFromBytes(
            fp.read(), use_builtin_types=use_builtin_types, dict_type=dict_type,
            huge_tree=False, resolve_entities=False
        )

    if fmt == _FORMAT_BINARY:
        return _BinaryPlistParser(use_builtin_types, dict_type).load(fp)

For more information on this vulnerability, you can refer to the following sources

1. Python Security Advisory
2. CVE-2022-48565 on the National Vulnerability Database

Conclusion: Protecting Your Application from XXE in Python
Developers must be extra cautious when handling XML data, as vulnerabilities like XXE can result in severe security threats. With the changes introduced in Python 3.9.2, this particular issue has been resolved in the plistlib module. However, it's essential for developers to always keep their applications updated, follow coding best practices, and stay informed about potential vulnerabilities in the languages and libraries they use. Keep checking Python's official security updates and vulnerability reports to protect your application from any future security threats.

Timeline

Published on: 08/22/2023 19:16:00 UTC
Last modified on: 10/11/2023 23:15:00 UTC