Today, we're going to take a deep dive into a recently discovered low-severity vulnerability, CVE-2024-7592, affecting CPython's standard library module 'http.cookies'. Although this vulnerability is only considered low in severity, it has the potential to cause excess CPU usage due to inefficient parsing of cookies that include backslashes for quoted characters. In this post, we'll explore the details of this vulnerability, its exploit, and references to the original research.

CVE-2024-7592: Overview and Impact

The CVE-2024-7592 vulnerability affects CPython, specifically the 'http.cookies' module in the standard library. When this module is used to parse cookies with backslashes for quoted characters in the cookie value, the parser employs an algorithm with quadratic complexity. As a result, parsing these cookies consumes an excessive amount of CPU resources, potentially leading to a slowdown in server performance or denial of service in extreme cases.

While this vulnerability is rated LOW severity, understanding and addressing it can help ensure your application runs optimally without unnecessary strain on your system resources.

Exploiting the Vulnerability: Code Snippet

To demonstrate the vulnerability, let's take a look at a code snippet that can exploit it. Assuming an attacker can control the value of the malicious_cookie variable, they can cause a higher than expected CPU usage by including backslashes for quoted characters in the cookie value:

import http.cookies

malicious_cookie = 'name="value\\\\\\\\\\\\\\\\\\\\"'
malicious_cookie_length = len(malicious_cookie)

cookie = http.cookies.SimpleCookie()
cookie.load(malicious_cookie)

print(f"Parsed cookie: {cookie}, length: {malicious_cookie_length}")

In this example, the algorithm handling the backslashes will consume more CPU resources than it should due to its quadratic complexity.

Mitigation and Patches

To mitigate this vulnerability, it is recommended to update your CPython installation to a version that includes a fix for this problem. Patches for this vulnerability have been submitted, and you can find them in the corresponding issue tracker, Issue #57898.

Applying these patches or updating CPython will remedy this issue and protect your application from potential slowdowns or denial of service.

You can find more information about this vulnerability by exploring the following references

1. CPython issue tracker that documents the vulnerability: Issue #57898
2. The CVE entry detailing the vulnerability: CVE-2024-7592
3. The patch submitted by the developer that addresses the issue: bpo-57898.patch

Conclusion

In this post, we've investigated the low-severity vulnerability CVE-2024-7592, which affects CPython's 'http.cookies' module, resulting in inefficient parsing of cookies containing backslashes for quoted characters. This vulnerability can lead to excessive CPU usage and has the potential to cause slowdowns or denial of service in extreme cases.

By understanding the details of this vulnerability and its exploit, along with applying any available patches or updates, you can prevent these negative outcomes and keep your application running smoothly.

Be sure to stay tuned for more insights into the world of cybersecurity, and remember that even low-severity vulnerabilities can be worth addressing to maintain the performance and security of your applications.

Timeline

Published on: 08/19/2024 19:15:08 UTC
Last modified on: 09/07/2024 02:45:03 UTC