How to Fix CVE-2024-20446 - A High Severity Denial of Service Vulnerability in Cisco NX-OS?

Cisco recently disclosed a critical denial of service (DoS) vulnerability in the DHCPv6 relay agent component of its NX-OS network operating system. This flaw, tracked as CVE-2024-20446, could allow an unauthenticated remote attacker to crash and reload affected Cisco switches, potentially leading to extended service disruptions. With a CVSS score of 8.6, this vulnerability poses a serious risk to organizations running vulnerable versions of Cisco NX-OS. In this article, we'll examine the details of CVE-2024-20446, its potential impact, affected products, and steps to mitigate and remediate this security issue.

What is Cisco NX-OS?

Cisco NX-OS is a network operating system designed for data center environments. It powers Cisco's Nexus series of switches and other data center networking products. Key features of NX-OS include:

NX-OS provides the core networking functionality for Cisco's data center switching portfolio, enabling scalable and flexible network architectures. It is widely deployed in enterprise and service provider data centers worldwide.

Summary of the Vulnerability

This vulnerability exists due to improper handling of specific fields in DHCPv6 RELAY-REPLY messages by the DHCPv6 relay agent component of Cisco NX-OS. The flaw stems from insufficient input validation of certain DHCPv6 packet fields.

An unauthenticated remote attacker could exploit this vulnerability by sending a specially crafted DHCPv6 packet to any IPv6 address configured on a vulnerable device. Successful exploitation would cause the dhcp_snoop process to repeatedly crash and restart, ultimately triggering a reload of the affected switch.

The root cause appears to be a NULL pointer dereference when processing malformed DHCPv6 relay reply messages. This aligns with the CWE-476 (NULL Pointer Dereference) weakness classification assigned by Cisco.

Impact of the Vulnerability

Successful exploitation of CVE-2024-20446 could allow an attacker to cause a denial of service condition on vulnerable Cisco Nexus switches. Specific impacts include:

Given that many organizations rely heavily on Cisco Nexus switches in their data center infrastructures, a targeted exploit of this vulnerability could significantly disrupt business operations. The ability for an unauthenticated remote attacker to trigger these effects makes this a particularly dangerous flaw.

Additionally, repeated exploitation could be used as part of a larger attack to keep network devices in a constant state of instability and unavailability. This could potentially be leveraged to bypass security controls or facilitate other malicious activities while network defenses are impaired.

Products Affected by the Vulnerability

The following Cisco products are vulnerable to CVE-2024-20446 when running affected NX-OS versions:

Devices are only vulnerable if they meet all of the following conditions:

Cisco has confirmed that the following products are not affected by this vulnerability:

How to Check if Your Product is Vulnerable

To determine if your Cisco Nexus switches are vulnerable to CVE-2024-20446, you need to check three key factors:

Here's how to check each of these:

1. Verify NX-OS Version

Log into the switch and use the show version command to check the running NX-OS version:

switch# show version
Cisco Nexus Operating System (NX-OS) Software
TAC support: http://www.cisco.com/tac
Copyright (c) 2002-2024, Cisco Systems, Inc. All rights reserved.
The copyrights to certain works contained in this software are
owned by other third parties and used and distributed under
license. Certain components of this software are licensed under
the GNU General Public License (GPL) version 2.0 or the GNU
Lesser General Public License (LGPL) Version 2.1. A copy of each
such license is available at
http://www.opensource.org/licenses/gpl-2.0.php and
http://www.opensource.org/licenses/lgpl-2.1.php

Software
  BIOS: version 07.69
  NXOS: version 9.3(9)
  BIOS compile time:  08/28/2024
  NXOS image file is: bootflash:///nxos.9.3.9.bin
  NXOS compile time:  8/15/2024 22:00:00 [08/16/2024 06:34:05]

If the version matches 8.2(11), 9.3(9), or 10.2(1), proceed to check the other conditions.

2. Check DHCPv6 Relay Agent Status

The DHCPv6 relay agent is enabled by default if the overall DHCP feature is enabled. To check its status, use the following command:

switch# show run all | include "^ipv6 dhcp relay"

If this command returns any output, the DHCPv6 relay agent is enabled. For example:

switch# show run all | include "^ipv6 dhcp relay"
ipv6 dhcp relay

3. Verify IPv6 Address Configuration

To check if any IPv6 addresses are configured on the device, use the show ipv6 interface brief command:

switch# show ipv6 interface brief
IPv6 Interface Status for VRF "default"(1)
Interface IPv6 Address/Link-local Address Interface Status
prot/link/admin
Eth1/50 2001:db8::1 up/up/up
fe80::a678:6ff:fed1:3e45

If this command shows any configured IPv6 addresses, your device meets all the conditions for vulnerability.

If your Cisco Nexus switch meets all three criteria - running a vulnerable NX-OS version, having DHCPv6 relay enabled, and at least one IPv6 address configured - it is potentially vulnerable to CVE-2024-20446.

How to Fix CVE-2024-20446

Cisco has released software updates to address this vulnerability. The primary recommended action is to upgrade to a fixed version of NX-OS. However, if immediate patching is not possible, there are some mitigation steps you can take.

Upgrade to Fixed NX-OS Versions

Cisco has released patches for the affected NX-OS versions. The following table shows the first fixed release for each affected version:

To upgrade your Cisco Nexus switches:

Temporary Mitigation

If you cannot immediately upgrade, you can mitigate the vulnerability by disabling the DHCPv6 relay agent if it's not required in your environment. To do this:

Please note that disabling the DHCPv6 relay agent may impact your network's DHCP functionality for IPv6. Ensure this change won't negatively affect your operations before implementing.

Additional Security Measures

While not directly addressing CVE-2024-20446, the following general security practices can help reduce the risk of exploitation:

Note: Using the Cisco Software Checker

To help customers determine their exposure to vulnerabilities in Cisco NX-OS Software, Cisco provides the Cisco Software Checker tool. This useful resource can identify:

To use the Cisco Software Checker:

Alternatively, you can use the form provided in Cisco security advisories to search for vulnerabilities affecting a specific software release.

This tool is invaluable for quickly assessing your exposure to known vulnerabilities and identifying the appropriate upgrade path to resolve multiple security issues simultaneously.

We hope this post helps explores the details of CVE-2024-20446, its summary, potential impact, and provide guidance on how to protect your Cisco Switches. Thanks for reading this post. Please share this post and help secure the digital world.Visit our website thesecmaster.com, and our social media page on Facebook, LinkedIn, Twitter, Telegram, Tumblr, Medium, and Instagram and subscribe to receive updates like this.

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