CVE-2023-20100
📋 TL;DR
An unauthenticated remote attacker can cause denial of service on Cisco wireless controllers by exploiting a logic error in the CAPWAP AP joining process. The attacker needs to add a malicious AP to the network and restart a legitimate AP under specific conditions. This affects Cisco IOS XE Software for Wireless LAN Controllers.
💻 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
Controller unexpectedly restarts, causing complete wireless network outage until device reboots
Likely Case
Intermittent controller restarts disrupting wireless connectivity for connected clients
If Mitigated
No impact if proper network segmentation and AP authentication controls are implemented
🎯 Exploit Status
Requires attacker to control both a malicious AP and be able to restart a legitimate AP
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Cisco IOS XE Software 17.9.4 or 17.10.1a and later
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-c9800-apjoin-dos-nXRHkt5
Restart Required: Yes
Instructions:
1. Download appropriate fixed software from Cisco Software Center. 2. Backup current configuration. 3. Upgrade to 17.9.4 or 17.10.1a or later. 4. Reboot controller to apply update.
🔧 Temporary Workarounds
Restrict AP Authentication
allImplement strict AP authentication policies to prevent unauthorized APs from joining
Network Segmentation
allSegment wireless management network to restrict access to CAPWAP ports
🧯 If You Can't Patch
- Implement strict physical and network access controls to prevent unauthorized AP connections
- Monitor for unauthorized AP join attempts and implement AP whitelisting
🔍 How to Verify
Check if Vulnerable:
Check controller version with 'show version' command and compare to affected versionsCheck Version:
show version | include VersionVerify Fix Applied:
Verify version is 17.9.4, 17.10.1a or later using 'show version' command📡 Detection & Monitoring
Log Indicators:
- Unexpected controller reboots
- Multiple AP join failures
- Unauthorized AP join attempts
Network Indicators:
- Unusual CAPWAP traffic patterns
- AP join requests from unknown MAC addresses
SIEM Query:
source="cisco-wlc" (event_type="reboot" OR event_type="ap_join_failure")