CVE-2022-20624: Cisco NX-OS CFSoIP DoS Vulnerability

CVE-2022-20624 Overview

A vulnerability in the Cisco Fabric Services over IP (CFSoIP) feature of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient validation of incoming CFSoIP packets. An attacker could exploit this vulnerability by sending crafted CFSoIP packets to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.

Critical Impact

Remote unauthenticated attackers can force affected Cisco Nexus switches and UCS Fabric Interconnects to reload, causing network outages and disrupting critical data center infrastructure.

Affected Products

• Cisco NX-OS Software (versions 7.0(3), 9.2(2), 9.2(3), 9.3(3), 9.3(5), and 4.1(1a)a)
• Cisco Nexus 3000 Series Switches (including 3048, 3132, 3164, 3172, 3232, 3264, 3408, 3432, 3464, 3524, 3548, 36180yc-r, 3636c-r)
• Cisco Nexus 9000 Series Switches (including 9236c, 9272q, 9316d-gx, 9332d-gx2b, 9348d-gx2a, 93600cd-gx, 9364d-gx2a, 92160yc-x, 92300yc, 92304qc, 92348gc-x, 9504, 9508, 9516)
• Cisco UCS Fabric Interconnects (UCS 64108, UCS 6454)

Discovery Timeline

• February 23, 2022 - CVE-2022-20624 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-20624

Vulnerability Analysis

This vulnerability affects the Cisco Fabric Services over IP (CFSoIP) feature, which is used to distribute configuration information across a fabric of Cisco devices over an IP network. CFSoIP enables seamless configuration synchronization between switches in a data center environment.

The vulnerability stems from improper input validation when processing incoming CFSoIP packets. When the CFSoIP feature is enabled on a device, it listens for incoming CFSoIP messages on a specific port. The packet processing logic fails to properly validate certain fields within the CFSoIP protocol data, allowing malformed packets to trigger an unhandled exception.

When exploited, this vulnerability causes the affected network device to reload completely, resulting in a denial of service condition. In data center environments where these switches serve as critical infrastructure, such a reload can cause significant network disruptions and affect dependent services.

Root Cause

The root cause of CVE-2022-20624 is improper input validation (CWE-20) combined with uncontrolled resource consumption (CWE-400) in the CFSoIP packet processing code. The NX-OS software does not adequately validate the structure and content of incoming CFSoIP packets before processing them. This lack of boundary checking and input sanitization allows specially crafted packets to trigger error conditions that the system cannot gracefully handle, leading to a system crash and subsequent reload.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying a target device running a vulnerable version of Cisco NX-OS with CFSoIP enabled
2. Crafting malicious CFSoIP packets with invalid or unexpected field values
3. Sending these packets to the target device over the network
4. The device's CFSoIP processing code encounters the malformed data and triggers an unhandled exception
5. The exception causes the device to reload, disrupting network connectivity

The attack can be launched from any network location that has IP connectivity to the management or in-band interfaces of the affected device where CFSoIP is enabled.

Detection Methods for CVE-2022-20624

Indicators of Compromise

• Unexpected device reloads or crashes with core dumps indicating CFSoIP-related processes
• Unusual network traffic patterns targeting CFSoIP ports from external or unexpected sources
• System log entries showing CFSoIP service errors or exceptions prior to device reboots
• Multiple consecutive device reloads within a short time period

Detection Strategies

• Monitor syslog messages for CFSoIP-related errors or crash notifications on Nexus and UCS devices
• Implement network intrusion detection rules to identify malformed or anomalous CFSoIP traffic
• Configure SNMP traps to alert on unexpected device reloads across the data center fabric
• Review crash logs and core dumps for evidence of CFSoIP packet processing failures

Monitoring Recommendations

• Enable detailed logging for CFSoIP services on all affected devices to capture error conditions
• Deploy network monitoring solutions to track device uptime and alert on unexpected reloads
• Implement baseline network traffic analysis to detect unusual CFSoIP communication patterns
• Configure centralized syslog collection for rapid correlation of events across multiple switches

How to Mitigate CVE-2022-20624

Immediate Actions Required

• Review the Cisco Security Advisory for complete details on affected versions and available patches
• Identify all Cisco Nexus and UCS devices running vulnerable NX-OS versions in your environment
• Prioritize patching for devices in critical network paths or high-availability configurations
• Implement network access controls to restrict CFSoIP traffic to trusted sources only

Patch Information

Cisco has released software updates that address this vulnerability. Administrators should consult the official Cisco Security Advisory for specific fixed software versions for their platform and current NX-OS release. The advisory contains detailed information about which software trains include the fix and provides guidance on upgrading affected devices.

Organizations should plan maintenance windows to apply the updates, considering the device reload required for NX-OS upgrades. For environments with high-availability configurations, rolling upgrades can minimize service disruption.

Workarounds

• Disable the CFSoIP feature if it is not required for your environment using the no cfs ipv4 distribute command
• Implement access control lists (ACLs) to restrict CFSoIP traffic to only trusted management networks
• Use Control Plane Policing (CoPP) to rate-limit CFSoIP traffic and mitigate potential exploitation attempts
• Segment network management traffic to isolated VLANs to reduce the attack surface

# Disable CFSoIP feature if not required
configure terminal
no cfs ipv4 distribute
end
copy running-config startup-config

# Alternative: Restrict CFSoIP with access control list
ip access-list CFSoIP-Restrict
  permit ip 10.0.0.0/8 any
  deny ip any any log
interface mgmt0
  ip access-group CFSoIP-Restrict in