CVE-2022-20856: Cisco IOS XE CAPWAP DoS Vulnerability

CVE-2022-20856 Overview

A vulnerability in the processing of Control and Provisioning of Wireless Access Points (CAPWAP) Mobility messages in Cisco IOS XE Wireless Controller Software for the Catalyst 9000 Family could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to a logic error and improper management of resources related to the handling of CAPWAP Mobility messages. An attacker could exploit this vulnerability by sending crafted CAPWAP Mobility packets to an affected device. A successful exploit could allow the attacker to exhaust resources on the affected device, causing the device to reload and resulting in a DoS condition.

Critical Impact

Unauthenticated remote attackers can cause network-wide wireless infrastructure disruption by forcing Catalyst 9800 series wireless controllers to reload through crafted CAPWAP Mobility packets.

Affected Products

• Cisco IOS XE (version 17.3.4c and related releases)
• Cisco Catalyst 9800 Wireless Controller
• Cisco Catalyst 9800-40 Wireless Controller
• Cisco Catalyst 9800-80 Wireless Controller
• Cisco Catalyst 9800-CL Cloud Wireless Controller
• Cisco Catalyst 9800-L Wireless Controller
• Cisco Catalyst 9800-L-C Wireless Controller
• Cisco Catalyst 9800-L-F Wireless Controller

Discovery Timeline

• 2022-09-30 - CVE-2022-20856 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-20856

Vulnerability Analysis

This vulnerability exists within the CAPWAP Mobility message handling functionality of Cisco IOS XE Wireless Controller Software. CAPWAP is a protocol used to manage wireless access points and their communication with wireless controllers. The Mobility feature enables seamless client roaming between different wireless controllers in a network.

The flaw stems from a logic error combined with improper resource management when processing CAPWAP Mobility messages. When the wireless controller receives specially crafted Mobility packets, it fails to properly validate and handle these messages, leading to resource exhaustion. This resource depletion ultimately causes the affected device to reload, disrupting all wireless network operations managed by that controller.

The vulnerability is particularly concerning for enterprise environments where Catalyst 9800 series controllers are deployed as centralized wireless management infrastructure. A successful attack would not only disrupt the controller but also disconnect all associated wireless access points and client devices.

Root Cause

The root cause of CVE-2022-20856 is categorized under CWE-664 (Improper Control of a Resource Through its Lifetime). The vulnerability arises from a logic error in the CAPWAP Mobility message processing code that fails to properly manage system resources. When processing crafted Mobility packets, the controller does not adequately track or limit resource allocation, allowing an attacker to trigger resource exhaustion through repeated malformed requests.

Attack Vector

The attack can be executed remotely over the network without requiring authentication or user interaction. An attacker needs network access to send CAPWAP protocol messages to the affected wireless controller. The CAPWAP protocol typically operates on UDP ports 5246 (control) and 5247 (data).

The exploitation mechanism involves:

1. Identifying a vulnerable Cisco Catalyst 9800 series wireless controller
2. Crafting malicious CAPWAP Mobility packets designed to trigger the logic error
3. Sending the crafted packets to the controller's CAPWAP service
4. The controller fails to properly handle the malformed messages
5. System resources become exhausted
6. The device reloads, causing a denial of service condition

The attack does not require prior knowledge of the network configuration beyond identifying the controller's IP address and ensuring network reachability to the CAPWAP service.

Detection Methods for CVE-2022-20856

Indicators of Compromise

• Unexpected wireless controller reboots or reloads without administrative action
• Unusual volume of CAPWAP traffic on UDP ports 5246 and 5247
• System logs showing resource exhaustion or memory-related errors preceding device reloads
• Multiple connected access points simultaneously losing controller connectivity

Detection Strategies

• Monitor CAPWAP protocol traffic for anomalous patterns or unusually high packet rates
• Implement network-based intrusion detection rules to identify malformed CAPWAP Mobility messages
• Configure SNMP traps and syslog monitoring to alert on unexpected device reloads
• Deploy network traffic analysis to baseline normal CAPWAP communication patterns

Monitoring Recommendations

• Enable detailed logging on Cisco Catalyst 9800 controllers to capture CAPWAP processing events
• Configure real-time alerting for controller availability status changes
• Implement network flow monitoring to detect unusual traffic patterns targeting wireless infrastructure
• Use SentinelOne Singularity XDR for comprehensive network visibility and anomaly detection across enterprise wireless infrastructure

How to Mitigate CVE-2022-20856

Immediate Actions Required

• Review the Cisco Security Advisory for affected software versions and apply recommended patches
• Implement network segmentation to restrict access to wireless controller management interfaces
• Configure access control lists (ACLs) to limit CAPWAP protocol traffic to authorized access points only
• Enable enhanced logging and monitoring on affected devices to detect exploitation attempts

Patch Information

Cisco has released software updates to address this vulnerability. Administrators should consult the Cisco Security Advisory (cisco-sa-c9800-mob-dos-342YAc6J) for specific fixed software versions and upgrade paths. Organizations should prioritize patching based on the criticality of their wireless infrastructure and exposure level.

Workarounds

• Restrict network access to CAPWAP ports (UDP 5246 and 5247) using firewall rules or ACLs
• Limit Mobility feature usage if not required for the deployment
• Implement network segmentation to isolate wireless controller management networks from untrusted segments
• Deploy redundant wireless controllers to minimize single points of failure during potential attacks

# Example ACL to restrict CAPWAP access to authorized access points only
# Apply on interface facing untrusted networks
access-list 110 permit udp host [AP_IP_ADDRESS] any eq 5246
access-list 110 permit udp host [AP_IP_ADDRESS] any eq 5247
access-list 110 deny udp any any eq 5246
access-list 110 deny udp any any eq 5247
access-list 110 permit ip any any