CVE-2021-1227
📋 TL;DR
This CSRF vulnerability in Cisco NX-OS NX-API allows unauthenticated remote attackers to trick authenticated users into executing malicious requests, potentially enabling configuration changes or data theft. Affected systems are Cisco Nexus switches running vulnerable NX-OS versions with NX-API enabled (disabled by default).
💻 Affected Systems
- Cisco Nexus 3000 Series Switches
- Cisco Nexus 9000 Series Switches in standalone NX-OS mode
- Cisco Nexus 9500 R-Series Line Cards and Fabric Modules
📦 What is this software?
Nx Os by Cisco
Nx Os by Cisco
Nx Os by Cisco
Nx Os by Cisco
Nx Os by Cisco
⚠️ Risk & Real-World Impact
Worst Case
Complete device takeover allowing attacker to reconfigure network, intercept traffic, or disable critical services
Likely Case
Unauthorized configuration changes leading to network disruption or data exposure
If Mitigated
No impact if NX-API is disabled or proper CSRF protections are implemented
🎯 Exploit Status
Exploitation requires social engineering to trick authenticated user into clicking malicious link while authenticated to NX-API
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: NX-OS Software releases 9.3(9), 10.2(4), 10.3(2) and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-nxapi-csrf-wRMzWL9z
Restart Required: Yes
Instructions:
1. Download appropriate fixed software from Cisco Software Center. 2. Backup configuration. 3. Upgrade to patched version following Cisco upgrade procedures. 4. Verify upgrade success and functionality.
🔧 Temporary Workarounds
Disable NX-API
allCompletely disable the vulnerable NX-API feature
configure terminal
no feature nxapi
copy running-config startup-config
Restrict NX-API Access
allLimit NX-API access to trusted networks only
configure terminal
nxapi http port 80
nxapi https port 443
nxapi certificate cert_name
copy running-config startup-config
🧯 If You Can't Patch
- Disable NX-API feature entirely if not required
- Implement network segmentation to restrict NX-API access to management networks only
🔍 How to Verify
Check if Vulnerable:
Check NX-OS version with 'show version' and verify if NX-API is enabled with 'show feature | include nxapi'Check Version:
show version | include "NXOS: version"Verify Fix Applied:
Verify upgraded version with 'show version' and confirm it's 9.3(9), 10.2(4), 10.3(2) or later📡 Detection & Monitoring
Log Indicators:
- Unexpected configuration changes via NX-API
- Authentication logs showing CSRF-like patterns
- NX-API access from unexpected sources
Network Indicators:
- HTTP/HTTPS requests to NX-API with suspicious referer headers
- NX-API requests originating from non-management networks
SIEM Query:
source="nxos" AND (event_type="configuration_change" OR event_type="nxapi_access") AND user_agent CONTAINS "malicious"