CVE-2020-3415
📋 TL;DR
This vulnerability in Cisco NX-OS Software allows an unauthenticated attacker on the same network segment to execute arbitrary code with administrative privileges or cause a denial of service by sending specially crafted Cisco Discovery Protocol packets. It affects Cisco Nexus switches and requires jumbo frames to be enabled on the receiving interface. Network administrators with Cisco Nexus devices in their infrastructure are affected.
💻 Affected Systems
- Cisco Nexus 3000 Series Switches
- Cisco Nexus 9000 Series Switches in standalone NX-OS mode
📦 What is this software?
Nx Os by Cisco
Nx Os by Cisco
⚠️ Risk & Real-World Impact
Worst Case
Full administrative compromise of affected network devices leading to complete network control, data exfiltration, or persistent backdoor installation.
Likely Case
Denial of service causing device reloads and network disruption, potentially leading to extended downtime.
If Mitigated
Limited to Layer 2 adjacent attackers only, with proper network segmentation reducing exposure significantly.
🎯 Exploit Status
Exploitation requires Layer 2 adjacency and jumbo frames enabled. The attacker needs to craft specific Cisco Discovery Protocol packets.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: NX-OS Software releases 9.3(5) and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-dme-rce-cbE3nhZS
Restart Required: Yes
Instructions:
1. Download the appropriate NX-OS Software release 9.3(5) or later from Cisco.com. 2. Upload the image to the switch. 3. Install the new image using 'install all' command. 4. Reload the device to complete the upgrade.
🔧 Temporary Workarounds
Disable jumbo frames on vulnerable interfaces
allPrevents exploitation by removing the required jumbo frames condition
interface <interface_name>
no system mtu jumbo
Disable Cisco Discovery Protocol
allCompletely prevents exploitation by disabling the vulnerable protocol
no cdp enable
🧯 If You Can't Patch
- Implement strict network segmentation to limit Layer 2 adjacency
- Deploy network monitoring to detect anomalous Cisco Discovery Protocol traffic
🔍 How to Verify
Check if Vulnerable:
Check NX-OS version with 'show version' and verify if running version prior to 9.3(5). Check if jumbo frames are enabled with 'show running-config interface'.Check Version:
show version | include NXOSVerify Fix Applied:
Verify NX-OS version is 9.3(5) or later using 'show version' command.📡 Detection & Monitoring
Log Indicators:
- Unexpected device reloads
- Cisco Discovery Protocol process crashes
- System log messages about protocol violations
Network Indicators:
- Anomalous Cisco Discovery Protocol packets
- Jumbo frame traffic to network devices
- Unusual traffic patterns from Layer 2 adjacent hosts
SIEM Query:
source="nxos_logs" AND ("reload" OR "crash" OR "CDP")