In the realm of web development, Tornado is known for being a reliable and efficient Python web framework and asynchronous networking library. It is widely used for building web applications and handling multiple user connections. However, in Tornado versions prior to 6.4.2, there exists a vulnerability, identified as CVE-2024-52804, which exposes the app to potential security threats as well as significant performance issues due to excessive CPU consumption while parsing cookies.

This post delves into the details of the vulnerability, discussing the underlying algorithm's inherent problem, its implications, and how Tornado 6.4.2 patches the issue. In addition, we will also provide a code snippet to showcase the problem, along with links to the original references and exploit details.

The Vulnerability (CVE-2024-52804)

The algorithm employed for parsing HTTP cookies in Tornado versions prior to 6.4.2 demonstrates quadratic complexity in some instances. In simple terms, this means that the time taken to execute the algorithm increases disproportionately as the size of the input increases. Consequently, when parsing cookies with maliciously-crafted headers, the CPU usage tends to spike, leading to a significant drop in the overall performance of the system.

To understand the extent of the problem, consider the following code snippet that demonstrates the issue:

import tornado.httpserver
import tornado.ioloop
import tornado.web

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world")

def make_app():
    return tornado.web.Application([
        (r"/", MainHandler),
    ])

if __name__ == "__main__":
    app = make_app()
    server = tornado.httpserver.HTTPServer(app)
    server.bind(8888)
    server.start()
    tornado.ioloop.IOLoop.current().start()

In this simple example, when a user connects to the web application, a "Set-Cookie" header is sent along with the HTTP response. Tornado parses this header to obtain the individual cookies. If a malicious user were to send a header with ill-formed cookies, the algorithm would take an excessive amount of time to parse the cookies, significantly increasing CPU usage and blocking the processing of other requests.

The Fix in Tornado 6.4.2

The release of Tornado 6.4.2 addresses this vulnerability by employing a more efficient algorithm for parsing HTTP cookies. This updated algorithm offsets the quadratic complexity problem, effectively reducing the risk of excessive CPU consumption when tackling malicious headers.

Upgrading to Tornado 6.4.2 is highly recommended to mitigate any risks associated with CVE-2024-52804. The installation can be done easily through pip:

pip install --upgrade tornado==6.4.2

For more information about the vulnerability and the fix, consult the following resources

- Original advisory from the Tornado project: Tornado Release 6.4.2
- CVE details: CVE-2024-52804
- Tornado GitHub repository: Tornado Framework

Conclusion

In conclusion, web applications configured to employ Tornado versions earlier than 6.4.2 are susceptible to performance issues and security vulnerabilities linked to the quadratic complexity of the HTTP cookie parsing algorithm. Upgrading to Tornado 6.4.2 is vital for eliminating the vulnerability CVE-2024-52804 and restoring the optimal performance of the system by employing an algorithm with improved efficiency.

Timeline

Published on: 11/22/2024 16:15:34 UTC