CVE-2021-34740
📋 TL;DR
An unauthenticated attacker on the same wireless network can send specially crafted 802.11 frames to Cisco Aironet Access Points, causing a memory leak that eventually triggers a device reboot and denial of service. This affects Cisco Aironet APs running vulnerable WLAN Control Protocol software. Organizations using these access points for wireless connectivity are impacted.
💻 Affected Systems
- Cisco Aironet Access Points
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Persistent DoS attacks could render wireless networks unavailable by repeatedly rebooting access points, disrupting business operations and connectivity.
Likely Case
Intermittent device reboots causing wireless network instability and connectivity drops for users.
If Mitigated
With proper network segmentation and monitoring, impact is limited to isolated wireless segments with quick detection and recovery.
🎯 Exploit Status
Exploitation requires wireless network adjacency but no authentication, making it relatively easy for attackers on the same network.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 17.3.4, 17.4.1, 17.5.1, 17.6.1 or later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-airo-wpa-pktleak-dos-uSTyGrL
Restart Required: Yes
Instructions:
1. Download appropriate firmware from Cisco Software Center. 2. Upload to AP via TFTP/SCP. 3. Reload AP to apply update. 4. Verify new version is running.
🔧 Temporary Workarounds
Wireless Network Segmentation
allIsolate vulnerable APs from critical networks using VLANs and firewall rules
Wireless Intrusion Prevention
allDeploy WIPS to detect and block malicious 802.11 frames
🧯 If You Can't Patch
- Implement strict wireless client isolation to limit attack surface
- Monitor AP logs for unexpected reloads and memory allocation failures
🔍 How to Verify
Check if Vulnerable:
Check AP firmware version via CLI: 'show version' and compare to vulnerable versions listed in Cisco advisoryCheck Version:
show version | include SoftwareVerify Fix Applied:
Verify firmware version is 17.3.4, 17.4.1, 17.5.1, 17.6.1 or later using 'show version' command📡 Detection & Monitoring
Log Indicators:
- Unexpected AP reloads
- Memory allocation failures
- WCP protocol errors
Network Indicators:
- Unusual 802.11 frame patterns
- Multiple AP reboots in short timeframe
SIEM Query:
source="cisco_ap" AND (event_type="reload" OR message="%MEMORY-3-ALLOCFAIL" OR message="%WCP-")