CVE-2023-20268: Cisco Wireless LAN Controller DoS Flaw

CVE-2023-20268 Overview

A vulnerability in the packet processing functionality of Cisco access point (AP) software could allow an unauthenticated, adjacent attacker to exhaust resources on an affected device. This vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption), affecting the fundamental resource management capabilities of Cisco wireless infrastructure.

This vulnerability stems from insufficient management of resources when handling certain types of traffic. An attacker could exploit this vulnerability by sending a series of specific wireless packets to an affected device. A successful exploit could allow the attacker to consume resources on an affected device, and a sustained attack could lead to the disruption of the Control and Provisioning of Wireless Access Points (CAPWAP) tunnel and intermittent loss of wireless client traffic.

Critical Impact

Successful exploitation can disrupt CAPWAP tunnel operations and cause intermittent wireless client traffic loss, potentially affecting enterprise network connectivity and availability.

Affected Products

• Cisco Wireless LAN Controller Software
• Cisco Catalyst 9800 Embedded Wireless Controller Firmware
• Cisco Catalyst 9800 Embedded Wireless Controller
• Cisco Business 150AX Firmware
• Cisco Business 150AX
• Cisco Business 151AXM Firmware
• Cisco Business 151AXM

Discovery Timeline

• 2023-09-27 - CVE-2023-20268 published to NVD
• 2024-12-12 - Last updated in NVD database

Technical Details for CVE-2023-20268

Vulnerability Analysis

This denial of service vulnerability targets the packet processing subsystem within Cisco access point software. The core issue lies in how the affected devices handle resource allocation when processing specific types of wireless packets. When an attacker transmits specially crafted wireless packets to a vulnerable access point, the device fails to properly manage and release resources, leading to gradual resource depletion.

The attack requires adjacent network access, meaning the attacker must be within wireless range of the affected access point. No authentication is required to exploit this vulnerability, and no user interaction is needed. The scope is changed, indicating that the vulnerable component impacts resources beyond its security scope—specifically affecting the CAPWAP control plane that manages wireless infrastructure.

The impact is primarily on availability, with no direct effect on confidentiality or integrity. However, the disruption of CAPWAP tunnels can have cascading effects on wireless network operations, potentially disconnecting multiple wireless clients and affecting business operations that depend on wireless connectivity.

Root Cause

The root cause of CVE-2023-20268 is insufficient resource management (CWE-400) in the packet processing functionality of Cisco access point software. When the access point receives certain types of wireless packets, it allocates system resources to process them but fails to properly release or limit these allocations. This allows an attacker to systematically exhaust available resources through repeated transmission of malicious packets.

The vulnerability specifically affects the mechanisms responsible for handling traffic that interacts with the CAPWAP protocol, which is critical for communication between access points and wireless LAN controllers. The lack of proper rate limiting or resource quotas for packet processing creates the conditions necessary for resource exhaustion attacks.

Attack Vector

The attack vector for CVE-2023-20268 is adjacent network access, which requires the attacker to be on the same network segment or within wireless range of the target access point. The attacker does not need any authentication credentials or special privileges to initiate the attack.

The exploitation process involves transmitting a series of specifically crafted wireless packets toward the vulnerable access point. These packets trigger the resource allocation flaw, causing the device to consume memory, processing cycles, or other system resources without proper cleanup. As the attack continues, available resources diminish until the access point can no longer maintain normal operations.

The vulnerability mechanism works by overwhelming the packet processing pipeline. Each malicious packet causes the access point to allocate resources that are not properly released, creating a memory or resource leak condition. When resources are exhausted, the CAPWAP tunnel—which maintains connectivity between the access point and the wireless LAN controller—becomes disrupted, leading to client disconnections and service interruptions.

Detection Methods for CVE-2023-20268

Indicators of Compromise

• Unusual wireless packet traffic patterns originating from specific MAC addresses or directions
• Elevated resource utilization (CPU, memory) on Cisco access points without corresponding legitimate traffic increase
• CAPWAP tunnel instability or frequent reconnection events logged on wireless LAN controllers
• Intermittent wireless client disconnections affecting multiple users simultaneously

Detection Strategies

• Monitor access point system resource utilization through SNMP or Cisco Prime Infrastructure for abnormal consumption patterns
• Implement wireless intrusion detection systems (WIDS) to identify unusual packet transmission patterns in the wireless environment
• Configure syslog alerting for CAPWAP tunnel state changes and reconnection events on both access points and wireless controllers
• Deploy network behavior analysis to baseline normal wireless traffic and alert on deviations

Monitoring Recommendations

• Enable detailed logging on Cisco wireless LAN controllers to capture CAPWAP tunnel events and access point health metrics
• Configure real-time alerts for access point resource utilization exceeding baseline thresholds
• Implement centralized monitoring of all affected Cisco access points and wireless controllers through Cisco DNA Center or similar platforms
• Correlate wireless controller logs with access point logs to identify patterns consistent with targeted resource exhaustion attacks

How to Mitigate CVE-2023-20268

Immediate Actions Required

• Review Cisco's Security Advisory to determine if your specific software versions are affected
• Inventory all Cisco access points, wireless LAN controllers, and Catalyst 9800 embedded wireless controllers in your environment
• Apply available software updates from Cisco that address this vulnerability
• Implement enhanced monitoring on affected devices to detect potential exploitation attempts

Patch Information

Cisco has released software updates that address this vulnerability. Administrators should consult the Cisco Security Advisory cisco-sa-ap-dos-capwap-DDMCZS4m for specific fixed software versions for each affected product. The advisory provides detailed guidance on determining affected versions and obtaining appropriate patches.

For Cisco Wireless LAN Controller Software, Catalyst 9800 Embedded Wireless Controller Firmware, and Cisco Business 150AX/151AXM firmware, ensure you are running a version that includes the fix for this vulnerability. Follow standard Cisco software upgrade procedures and test in a non-production environment before deploying to production infrastructure.

Workarounds

• No specific workarounds are documented by Cisco for this vulnerability; patching is the recommended remediation
• Implement wireless security best practices including RF segmentation and reduced power levels to limit attacker proximity opportunities
• Consider deploying additional access points to provide redundancy in case individual APs experience resource exhaustion
• Enable wireless intrusion prevention features where available to detect and potentially mitigate malicious wireless traffic

# Example: Check current software version on Cisco WLC
# Connect to WLC CLI and verify version against advisory
show sysinfo

# Example: Monitor CAPWAP tunnel status
show ap join stats summary all

# Example: Check AP resource utilization
show ap summary