CVE-2023-6596 - The Rapid Reset Patch That Wasn’t Enough for OpenShift Containers

In late 2023, the world of containerized cloud solutions was rocked by the disclosure of the Rapid Reset vulnerability (CVE-2023-44487 and CVE-2023-39325). This vulnerability allowed attackers to overwhelm and crash web servers by abusing HTTP/2’s rapid stream resets, causing widespread headaches for major platforms, including OpenShift by Red Hat.

Soon after, vendors rushed to ship fixes. But as we drifted into 2024, researchers discovered an incomplete patch—now tracked as CVE-2023-6596—that left OpenShift's container platform vulnerable even *after* admins thought they were protected.

Let’s break down what happened, see some proof-of-concept code, and learn why CVE-2023-6596 is a textbook case of why “fix” doesn’t always mean “safe”.

## The Road So Far: HTTP/2 Rapid Reset Vulnerability

HTTP/2 was designed to make websites faster and more efficient. But, like most good things, it has been found to be double-edged. The original vulnerability, CVE-2023-44487, or *Rapid Reset*, allowed remote attackers to flood the server with many HTTP/2 streams that were immediately reset. This rains down reset signals on the server, eventually overwhelming it and causing denial of service (DoS).

The Exploit, in Simple Terms

Here’s the trick: Every time the server processes a new HTTP/2 stream, it allocates resources. If an attacker opens thousands of new streams and cancels all of them in rapid sequence (using RST_STREAM frames), the server’s CPU and memory are chewed up, until everything grinds to a halt.

OpenShift (which uses popular web servers such as Envoy Proxy and NGINX) was as vulnerable as anyone.

The Incomplete Fix: Welcome, CVE-2023-6596

After emergency patches were issued, Red Hat and others thought they’d plugged the hole. But a closer look revealed a critical mistake in the patch logic delivered for several OpenShift Container versions.

What Was Missed?

The original patch tried to limit how many reset streams could be made in a short interval, but it failed to account for inherited stream resources among certain types of requests—especially when containers were networked together in clusters.

Attackers found they could *still* overwhelm the server with rapid resets, just using slightly tweaked requests.

Reference:
- Red Hat Issue Tracker for CVE-2023-6596
- OpenShift Advisory

PoC: How Could You Trigger This (for Test Purposes Only)?

Below is a Python snippet that demonstrates how an attacker might still overload a patched OpenShift Container environment—*if* CVE-2023-6596 is unpatched.

Warning: DO NOT run this code against servers you do not own or have explicit permission to test.

import httpx
import time

# Replace with your vulnerable OpenShift service endpoint
target = "https://vulnerable-openshift.example.com";

def rapid_reset_flood(target, streams=100, delay=.002):
    with httpx.Client(http2=True, verify=False) as client:
        for i in range(streams):
            try:
                r = client.post(target, headers={"x-test-stream": str(i)})
                # Immediately send another request to trigger rapid use/reset
            except Exception as err:
                print(f"Exception at stream {i}: {err}")
            time.sleep(delay)  # tiny delay to stack up the streams

if __name__ == "__main__":
    rapid_reset_flood(target)

This example attempts to rapidly establish and reset HTTP/2 streams. If the patch is incomplete, the server may hit its resource limits or fail.

How Do You Fix This for Real?

Vendors have since provided updated patches making sure that *all* forms of rapid reset, including inherited and inter-container streaming, are throttled.

If You’re an OpenShift Admin

- Patch NOW: Make sure you have the latest version. Check Red Hat Security Updates for CVE-2023-6596.
- Monitor HTTP/2 stream activity in your gateway logs; look for spikes in RST_STREAM frames.
- Consider disabling HTTP/2 on external interfaces if you don’t need it—fall back to HTTP/1.1 temporarily.

A patch isn’t always a fix. Rushed code reviews and incomplete testing can leave holes.

2. HTTP/2 is complex. DoS vulnerabilities can hide in protocol edge cases.
3. Monitor CVEs, not just patches. If a new CVE appears for a problem you thought was solved (like CVE-2023-6596, after CVE-2023-44487!), reassess your defenses.

TL;DR

CVE-2023-6596 proves that sometimes the most dangerous bugs are the ones we thought we already fixed. If you use OpenShift Containers, make sure your nodes are up-to-date, and keep an eye on your HTTP/2 traffic. Security is a journey, not a checkbox.

Stay patched and stay safe!

*This post was written exclusively for readers who want plain-English, practical insights on emerging container vulnerabilities. Spread awareness, but practice ethical security!*

Timeline

Published on: 04/25/2024 16:15:10 UTC
Last modified on: 04/25/2024 17:24:59 UTC