CVE-2021-1565
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to crash Cisco Catalyst 9000 wireless controllers by sending malformed CAPWAP protocol packets, causing denial of service. It affects Cisco IOS XE software on Catalyst 9000 Family Wireless Controllers. The vulnerability stems from insufficient packet validation in CAPWAP protocol processing.
💻 Affected Systems
- Cisco Catalyst 9000 Family 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 →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 →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 →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 →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 →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 device crash and reload causing extended network downtime for wireless services, potentially affecting all connected wireless access points and clients.
Likely Case
Intermittent device crashes and reloads disrupting wireless connectivity for connected clients until the device restarts.
If Mitigated
No impact if devices are patched or properly segmented from untrusted networks.
🎯 Exploit Status
The advisory does not mention public exploits, but the low complexity and unauthenticated nature make weaponization likely.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Cisco Security Advisory for specific fixed releases for each affected version
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ewlc-capwap-dos-gmNjdKOY
Restart Required: Yes
Instructions:
1. Check current IOS XE version on affected Catalyst 9000 wireless controllers. 2. Review Cisco Security Advisory for fixed releases matching your deployment. 3. Download and install the appropriate fixed release from Cisco Software Center. 4. Reload the device to apply the update.
🔧 Temporary Workarounds
Network Segmentation
allRestrict access to CAPWAP ports (UDP 5246, 5247) to trusted management networks only.
access-list 100 permit udp <trusted_networks> any eq 5246
access-list 100 permit udp <trusted_networks> any eq 5247
access-list 100 deny udp any any eq 5246
access-list 100 deny udp any any eq 5247
interface <interface>
ip access-group 100 in
🧯 If You Can't Patch
- Implement strict network access controls to limit CAPWAP traffic to authorized management networks only.
- Deploy intrusion prevention systems (IPS) with signatures for CAPWAP protocol anomalies if available.
🔍 How to Verify
Check if Vulnerable:
Check IOS XE version on Catalyst 9000 wireless controllers: 'show version' and compare against vulnerable versions in Cisco advisory.Check Version:
show version | include VersionVerify Fix Applied:
After patching, verify the installed version is listed as fixed in the Cisco advisory and test CAPWAP functionality.📡 Detection & Monitoring
Log Indicators:
- Device crash and reload logs
- CAPWAP protocol errors or malformed packet warnings
- System instability messages
Network Indicators:
- Unexpected CAPWAP traffic from untrusted sources
- Multiple malformed CAPWAP packets to UDP ports 5246/5247
SIEM Query:
source="catalyst_logs" AND ("reload" OR "crash" OR "CAPWAP error")