CVE-2021-1615
📋 TL;DR
An unauthenticated remote attacker can cause denial of service on Cisco Catalyst Access Points by sending crafted traffic that exhausts buffer resources. This affects Cisco Embedded Wireless Controller software on Catalyst APs, disrupting both AP functionality and client traffic.
💻 Affected Systems
- Cisco Catalyst 9100, 9115, 9117, 9120, 9130, 9136 Series Access Points
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete AP outage affecting all wireless clients, requiring physical reboot to restore service
Likely Case
Intermittent service disruption affecting multiple clients until attack traffic stops
If Mitigated
Minimal impact with proper network segmentation and traffic filtering
🎯 Exploit Status
Attack requires sending crafted packets to vulnerable APs; no authentication needed
🛠️ 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-iosxe-ewc-dos-g6JruHRT
Restart Required: Yes
Instructions:
1. Download appropriate fixed software from Cisco Software Center. 2. Upload to AP. 3. Reload AP to apply update. 4. Verify new version is running.
🔧 Temporary Workarounds
Network Segmentation
allIsolate AP management interfaces from untrusted networks
ACL Filtering
allImplement access control lists to restrict traffic to AP management interfaces
access-list 100 deny ip any host <AP_IP>
access-list 100 permit ip any any
🧯 If You Can't Patch
- Implement strict network segmentation to isolate APs from untrusted networks
- Deploy intrusion prevention systems to detect and block crafted packet attacks
🔍 How to Verify
Check if Vulnerable:
Check AP software version with 'show version' command and compare to affected versionsCheck Version:
show version | include VersionVerify Fix Applied:
Verify AP is running IOS XE 17.3.4, 17.6.1, 17.7.1 or later via 'show version'📡 Detection & Monitoring
Log Indicators:
- AP crash logs
- Memory exhaustion warnings
- High packet drop rates
Network Indicators:
- Unusual traffic patterns to AP management interfaces
- Sudden loss of wireless connectivity
SIEM Query:
source="ap_logs" AND ("crash" OR "memory" OR "resource")