CVE-2021-1437
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to download any file from Cisco Aironet access points via TFTP due to an unrestricted configuration. Affected organizations using vulnerable Cisco Aironet APs with FlexConnect Upgrade feature enabled are at risk of information disclosure.
💻 Affected Systems
- Cisco Aironet Series Access Points
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers obtain sensitive configuration files, credentials, or cryptographic materials leading to full network compromise.
Likely Case
Attackers download configuration files containing network topology, passwords, or other sensitive operational data.
If Mitigated
Limited to non-sensitive file access if proper network segmentation and access controls are implemented.
🎯 Exploit Status
Simple TFTP request required. No authentication needed. Exploitation trivial for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Cisco Aironet Access Points Software Release 8.10.151.0 and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-aironet-info-disc-BfWqghj
Restart Required: Yes
Instructions:
1. Download software release 8.10.151.0 or later from Cisco.com. 2. Upload to AP via TFTP/SCP. 3. Reload AP to apply update. 4. Verify new version is running.
🔧 Temporary Workarounds
Disable FlexConnect Upgrade Feature
allDisable the vulnerable feature if not required for operations
configure terminal
no flexconnect upgrade enable
end
write memory
Restrict TFTP Access
allImplement ACLs to restrict TFTP access to trusted management networks only
configure terminal
access-list 100 permit tcp <trusted_network> any eq tftp
access-list 100 deny ip any any
interface <ap_interface>
ip access-group 100 in
end
write memory
🧯 If You Can't Patch
- Segment AP management interfaces from user/data networks using VLANs or physical separation
- Implement strict firewall rules blocking TFTP (port 69) from untrusted networks to APs
🔍 How to Verify
Check if Vulnerable:
Check AP software version: 'show version' and verify if below 8.10.151.0. Check FlexConnect status: 'show flexconnect summary'.Check Version:
show version | include SoftwareVerify Fix Applied:
Verify AP software version is 8.10.151.0 or later using 'show version'. Confirm TFTP access restrictions are in place.📡 Detection & Monitoring
Log Indicators:
- TFTP requests from unexpected sources in AP logs
- Unauthorized file access attempts
Network Indicators:
- TFTP traffic (UDP port 69) to APs from non-management networks
- Unusual file transfer patterns
SIEM Query:
source_port:69 AND destination_ip:<AP_IP_range> AND NOT source_ip:<management_network>