CVE-2020-3494
📋 TL;DR
This vulnerability allows an unauthenticated attacker on the same network segment to send specially crafted CAPWAP packets to Cisco Catalyst 9800 Series Wireless Controllers running vulnerable IOS XE software, causing the device to crash and reload. This results in a denial of service condition affecting wireless network availability. Only adjacent attackers can exploit this vulnerability.
💻 Affected Systems
- Cisco Catalyst 9800 Series Wireless Controllers
📦 What is this software?
Ios Xe by Cisco
Cisco IOS XE is Cisco's modern network operating system running on enterprise routers, switches, and wireless controllers deployed across corporate networks, data centers, branch offices, and service provider infrastructure worldwide. As the evolution of Cisco IOS, IOS XE provides a Linux-based modu...
Learn more about Ios Xe →⚠️ Risk & Real-World Impact
Worst Case
Complete wireless network outage as the controller crashes and reloads, disrupting all wireless connectivity until the device restarts.
Likely Case
Intermittent wireless service disruptions as attackers trigger repeated crashes, causing availability issues for connected devices.
If Mitigated
Limited impact if network segmentation prevents adjacent attacker access to CAPWAP traffic or if patches are applied.
🎯 Exploit Status
Exploitation requires sending malformed CAPWAP packets but does not require authentication. Attackers need to be on the same network segment as the target.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Cisco IOS XE Software releases 16.12.4, 17.3.3, 17.6.1 or later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-capwap-dos-TPdNTdyq
Restart Required: Yes
Instructions:
1. Download appropriate fixed software version from Cisco Software Center. 2. Backup current configuration. 3. Install the update following Cisco IOS XE upgrade procedures. 4. Reboot the device to load the new software.
🔧 Temporary Workarounds
Network Segmentation
allRestrict access to CAPWAP traffic by implementing network segmentation and access control lists to limit which devices can communicate with the wireless controller on CAPWAP ports.
access-list 100 deny ip any host <controller-ip> eq 5246
access-list 100 deny ip any host <controller-ip> eq 5247
access-list 100 permit ip any any
🧯 If You Can't Patch
- Implement strict network segmentation to isolate wireless controller management traffic from untrusted network segments.
- Deploy intrusion prevention systems (IPS) to detect and block malformed CAPWAP packets.
🔍 How to Verify
Check if Vulnerable:
Check IOS XE version with 'show version' command and compare against vulnerable releases (prior to 16.12.4, 17.3.3, 17.6.1).Check Version:
show version | include VersionVerify Fix Applied:
Verify the device is running fixed version (16.12.4, 17.3.3, 17.6.1 or later) using 'show version' command.📡 Detection & Monitoring
Log Indicators:
- Unexpected device reloads or crashes in system logs
- CAPWAP protocol errors or malformed packet warnings
- High CPU or memory usage preceding crashes
Network Indicators:
- Unusual CAPWAP traffic patterns from unexpected sources
- Multiple malformed CAPWAP packets to controller ports 5246/5247
SIEM Query:
source="catalyst9800" AND (event_type="crash" OR event_type="reload") OR (protocol="CAPWAP" AND packet_size>normal_threshold)