CVE-2026-20048
📋 TL;DR
An authenticated remote attacker can cause a denial of service (DoS) on Cisco Nexus 9000 Series Fabric Switches in ACI mode by sending continuous SNMP queries to a specific MIB. This triggers improper SNMP request parsing, leading to kernel panic and device reload. The vulnerability affects SNMPv1, v2c, and v3, requiring valid read-only community strings (v1/v2c) or user credentials (v3).
💻 Affected Systems
- Cisco Nexus 9000 Series Fabric Switches
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete device outage requiring manual reboot, disrupting network operations for all connected systems.
Likely Case
Targeted DoS attack causing service disruption until device automatically reloads (typically minutes).
If Mitigated
Minimal impact with proper SNMP access controls and monitoring in place.
🎯 Exploit Status
Exploitation requires SNMP authentication but is straightforward once credentials are obtained. No special tools needed beyond standard SNMP clients.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco advisory for specific fixed releases
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-dsnmp-cNN39Uh
Restart Required: Yes
Instructions:
1. Review Cisco advisory for specific fixed releases. 2. Schedule maintenance window. 3. Backup configuration. 4. Upgrade to patched NX-OS version. 5. Verify SNMP functionality post-upgrade.
🔧 Temporary Workarounds
Restrict SNMP Access
allLimit SNMP access to trusted management stations using ACLs
snmp-server community <string> ro <acl-name>
snmp-server user <username> auth <algorithm> <password> priv <algorithm> <password> access <acl-name>
Disable SNMP if Not Required
allCompletely disable SNMP service if not needed for monitoring
no snmp-server enable
🧯 If You Can't Patch
- Implement strict SNMP access control lists (ACLs) to limit access to essential management stations only
- Monitor SNMP traffic for unusual patterns and implement rate limiting where possible
🔍 How to Verify
Check if Vulnerable:
Check device model and operating mode: 'show version' and 'show aci fabric' to confirm Nexus 9000 in ACI modeCheck Version:
show versionVerify Fix Applied:
Verify running patched version: 'show version | include NX-OS' and compare with Cisco advisory fixed releases📡 Detection & Monitoring
Log Indicators:
- High frequency of SNMP requests from single source
- Device reload messages in system logs
- SNMP authentication failures followed by high request volume
Network Indicators:
- Unusual SNMP traffic patterns to specific MIBs
- High volume of SNMP Get/GetNext requests
SIEM Query:
source="nexus_logs" ("kernel panic" OR "reload" OR "%SNMP-3-AUTHFAIL") AND "SNMP"