CVE-2021-34768
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to crash Cisco Catalyst 9000 wireless controllers by sending malformed CAPWAP packets, causing denial of service. It affects Cisco IOS XE Software running on Catalyst 9000 Family Wireless Controllers. The vulnerability exists due to insufficient validation of CAPWAP protocol packets.
💻 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 →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 wireless network outage until manual intervention.
Likely Case
Intermittent DoS affecting wireless connectivity as devices crash and reload automatically.
If Mitigated
Limited impact with proper network segmentation and monitoring to detect and block malicious CAPWAP traffic.
🎯 Exploit Status
Exploitation requires sending specially crafted CAPWAP packets to vulnerable devices.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Cisco IOS XE Software releases 17.3.4, 17.6.1, 17.7.1 or later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ewlc-capwap-dos-gmNjdKOY
Restart Required: Yes
Instructions:
1. Download appropriate fixed software version from Cisco Software Center. 2. Backup current configuration. 3. Upgrade to fixed release following Cisco IOS XE upgrade procedures. 4. Verify successful upgrade and functionality.
🔧 Temporary Workarounds
CAPWAP Access Control
allRestrict CAPWAP traffic to trusted sources using access control lists.
access-list 100 permit udp host <trusted-ap-ip> host <controller-ip> eq 5246
access-list 100 deny udp any any eq 5246
interface <controller-interface>
ip access-group 100 in
🧯 If You Can't Patch
- Implement strict network segmentation to isolate wireless controllers from untrusted networks.
- Deploy intrusion prevention systems to detect and block malformed CAPWAP packets.
🔍 How to Verify
Check if Vulnerable:
Check IOS XE version with 'show version' command and compare to affected versions.Check Version:
show version | include VersionVerify Fix Applied:
Verify running version is 17.3.4, 17.6.1, 17.7.1 or later using 'show version' command.📡 Detection & Monitoring
Log Indicators:
- Unexpected device reloads
- CAPWAP protocol errors
- System crash dumps
Network Indicators:
- Unusual CAPWAP traffic patterns
- UDP port 5246 traffic from untrusted sources
SIEM Query:
source="cisco-ios" (reload OR crash OR "CAPWAP error")