In this post, we will discuss a recent vulnerability identified with the Common Vulnerabilities and Exposures (CVE) designation CVE-2024-11168. The vulnerability is related to the improper validation of hosts enclosed within brackets ([]) in the urllib.parse.urlsplit() and urlparse() functions of Python's standard library. Ideally, these functions should only allow square-bracketed hosts to be IPv6 or IPvFuture addresses. However, this vulnerability allows hosts within brackets that are neither IPv6 nor IPvFuture. This behavior not only goes against RFC 3986 standards, but it also potentially enables Server-Side Request Forgery (SSRF) attacks when a URL is processed by multiple URL parsers.
In this post, we will provide an explanation of the vulnerability, demonstrate how the misuse of brackets can lead to exploitation, and highlight where you can find patches and more information about this CVE.
Description of the issue
The urllib.parse.urlsplit() and urlparse() functions in Python's standard library are commonly used to parse URLs, separating their components such as the scheme, authority, path, query, and fragment. When these functions encounter a host enclosed within square brackets ([]), they are supposed to ensure that the host is a valid IPv6 or IPvFuture address, according to the RFC 3986 standard.
RFC 3986 is an Internet Engineering Task Force (IETF) standard that provides guidance on the generic syntax for Uniform Resource Identifiers (URIs). It specifies that bracketed literals ([]) are reserved for use with IPv6 and IPvFuture addresses.
However, due to an implementation bug, the urlsplit() and urlparse() functions do not properly validate the content within square brackets, allowing hosts that are neither IPv6 nor IPvFuture addresses. This can lead to inconsistencies when processing URLs with multiple URL parsers and open the door for potential SSRF attacks.
Example of vulnerability
To illustrate the vulnerability, here is a simple code snippet that demonstrates the misuse of brackets with Python's urllib.parse.urlsplit() function:
from urllib.parse import urlsplit
url = "http://[example.com]/path?query=value#fragment";
parsed_url = urlsplit(url)
print(parsed_url)
Output
SplitResult(scheme='http', netloc='[example.com]', path='/path', query='query=value', fragment='fragment')
As we can see, the urlsplit() function does not throw an error for the URL containing an invalid bracketed host "example.com." Instead, it successfully parses the components of the URL as if it were a valid URI.
For more details on this vulnerability, you can refer to the following sources
1. The CVE information and details: CVE-2024-11168
2. The Python issue tracker discussion: Issue 44956
3. The associated Python security advisory: Python Security Advisory
Exploitation details
The exploitation of this vulnerability hinges on a URL being processed by multiple URL parsers, some of which might not make the same assumptions as urllib.parse.urlsplit() and urlparse() functions. An attacker, knowing which parser would utilize the improperly validated bracketed host, could craft a URL that seems innocuous but in fact points to a different server, enabling an SSRF attack.
Such an attack can have serious consequences, as it may expose sensitive information, instigate an internal security breach, and potential data leakage.
Patching the vulnerability
To mitigate the risk associated with this vulnerability, it is recommended to update your Python installation to the latest version, which includes the appropriate patches. This should ensure that the urlsplit() and urlparse() functions conform to the RFC 3986 standard and validate bracketed IPv6 and IPvFuture addresses."""
In conclusion, CVE-2024-11168 highlights the importance of proper validation in URL parsing functions and the risks associated with non-conformance to established standards. By staying informed about this vulnerability, its effects, and updates to Python, you can help ensure the security of your applications and systems.
Timeline
Published on: 11/12/2024 22:15:14 UTC
Last modified on: 01/06/2025 18:15:17 UTC