CVE-2022-20625: Cisco FXOS Discovery Protocol DoS Flaw

CVE-2022-20625 Overview

A vulnerability in the Cisco Discovery Protocol (CDP) service of Cisco FXOS Software and Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to cause the service to restart, resulting in a denial of service (DoS) condition. This vulnerability is due to improper handling of Cisco Discovery Protocol messages that are processed by the CDP service. An attacker could exploit this vulnerability by sending a series of malicious Cisco Discovery Protocol messages to an affected device. A successful exploit could allow the attacker to cause the Cisco Discovery Protocol service to fail and restart. In rare conditions, repeated failures of the process could occur, which could cause the entire device to restart.

Critical Impact

An unauthenticated attacker on an adjacent network segment can cause CDP service restarts, potentially leading to complete device reboots and network disruption across critical Cisco infrastructure including Nexus switches, Firepower appliances, MDS storage switches, and UCS fabric interconnects.

Affected Products

• Cisco Firepower Extensible Operating System (FXOS)
• Cisco NX-OS Software
• Cisco Nexus 3000, 7000, 7700, and 9000 Series Switches
• Cisco Firepower 4100 and 9300 Series Appliances
• Cisco MDS 9000 Series Multilayer Switches
• Cisco UCS 6200, 6300, and 6400 Series Fabric Interconnects
• Cisco Nexus 1000V and 1000VE Virtual Switches

Discovery Timeline

• February 23, 2022 - CVE-2022-20625 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-20625

Vulnerability Analysis

This vulnerability exists in the Cisco Discovery Protocol service implementation across multiple Cisco network operating systems. CDP is a Layer 2 protocol used by Cisco devices to share information about directly connected Cisco equipment. The vulnerability stems from improper input validation and error handling when the CDP service processes incoming protocol messages.

When an affected device receives specially crafted CDP packets, the CDP service fails to properly validate or handle certain message structures. This improper handling causes the service process to crash and restart. While a single service restart may cause minimal disruption, persistent exploitation through repeated malicious packets can trigger cascading failures that result in a full device reload.

The attack requires Layer 2 adjacency, meaning the attacker must be on the same network segment or VLAN as the target device. This limits the attack surface to internal network actors or those who have compromised adjacent network devices. However, given that CDP is enabled by default on most Cisco platforms and operates on virtually all interfaces, the vulnerability affects a broad range of deployment scenarios across enterprise data centers, campus networks, and virtualized environments.

Root Cause

The root cause is improper handling of Cisco Discovery Protocol messages within the CDP service. The service lacks adequate input validation and error recovery mechanisms when processing malformed or unexpected CDP packet structures. This falls under CWE-399 (Resource Management Errors), indicating that the software does not properly manage system resources when encountering anomalous protocol data.

Attack Vector

The attack vector is adjacent network access, requiring the attacker to be on the same Layer 2 broadcast domain as the target device. The attacker sends a series of specially crafted CDP packets to the target device's CDP-enabled interfaces. No authentication is required, and the attack does not require any user interaction.

The exploitation flow involves:

1. Attacker gains access to a network segment where CDP traffic can reach the target device
2. Attacker crafts malicious CDP messages designed to trigger the parsing vulnerability
3. Malicious CDP packets are transmitted to the target device
4. The CDP service on the target device improperly handles the packets and crashes
5. Repeated exploitation can cause the entire device to restart

Detection Methods for CVE-2022-20625

Indicators of Compromise

• Unexpected CDP service restarts logged in system messages (e.g., %CDP-4-RESTART or similar syslog events)
• Increased frequency of CDP-related process crashes in the device's core dump or crashinfo logs
• Unusual CDP packet rates or malformed CDP packets captured in network traffic analysis
• Device uptime resets without administrator-initiated reboots

Detection Strategies

• Monitor syslog messages for CDP service restart events and correlate with network traffic anomalies
• Implement network-based intrusion detection rules to identify malformed or excessive CDP packets on Layer 2 segments
• Configure SNMP traps to alert on process crashes and unexpected device reboots
• Use SentinelOne Singularity for network device visibility and anomaly detection across hybrid infrastructure

Monitoring Recommendations

• Enable detailed logging for CDP events and forward logs to a centralized SIEM for correlation
• Establish baseline CDP traffic patterns and alert on deviations indicating potential exploitation attempts
• Monitor affected devices for unexpected reboots or service disruptions during normal operations
• Implement Layer 2 traffic visibility tools to inspect CDP packet contents on critical network segments

How to Mitigate CVE-2022-20625

Immediate Actions Required

• Apply the appropriate security patches from Cisco as documented in the Cisco Security Advisory
• Disable CDP on interfaces where it is not required, particularly on ports facing untrusted network segments
• Implement network segmentation to limit Layer 2 adjacency attack surfaces
• Review and audit which interfaces have CDP enabled across your Cisco infrastructure

Patch Information

Cisco has released software updates that address this vulnerability. Administrators should consult the Cisco Security Advisory cisco-sa-cdp-dos-G8DPLWYG to determine the appropriate fixed software release for their specific platform and current software version. The advisory provides detailed version-specific information for FXOS, NX-OS, and all affected hardware platforms.

Workarounds

• Disable CDP globally or on specific interfaces where neighbor discovery is not operationally required using the no cdp enable interface command or no cdp run global command
• Implement Layer 2 access control lists (ACLs) where supported to filter CDP traffic from untrusted sources
• Use LLDP (Link Layer Discovery Protocol) as an alternative where CDP functionality is needed but can be replaced
• Deploy private VLANs or port isolation features to limit Layer 2 communication between potentially compromised hosts and network infrastructure

# Disable CDP on a specific interface
interface Ethernet1/1
  no cdp enable

# Disable CDP globally on the device
no cdp run

# Verify CDP status
show cdp interface
show cdp neighbors