CVE-2024-20371
📋 TL;DR
A vulnerability in Cisco Nexus 3550-F Switches allows unauthenticated remote attackers to bypass ACL deny rules during device reboot, sending traffic to the management interface that should be blocked. This affects organizations using these switches with ACLs configured to restrict management interface access.
💻 Affected Systems
- Cisco Nexus 3550-F 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
Attackers could gain unauthorized access to the management interface during reboot windows, potentially compromising switch configuration or using it as a pivot point into the network.
Likely Case
Attackers could probe or attack the management interface during maintenance windows when reboots occur, though they would still need valid credentials or additional vulnerabilities to achieve full compromise.
If Mitigated
With proper network segmentation and additional firewall rules, the impact is limited to potential reconnaissance or denial-of-service against the management interface.
🎯 Exploit Status
Exploitation requires timing with device reboots and knowledge of the management interface IP. No authentication required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Cisco advisory for specific fixed versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-3550-acl-bypass-mhskZc2q
Restart Required: Yes
Instructions:
1. Review Cisco advisory for fixed software versions. 2. Download and install the appropriate fixed software from Cisco. 3. Reboot the switch to apply the update.
🔧 Temporary Workarounds
Schedule reboots during maintenance windows
allPerform device reboots only during scheduled maintenance periods when network monitoring is heightened.
Implement additional firewall rules
allAdd firewall rules upstream to block unauthorized access to switch management interfaces.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate management interfaces from untrusted networks
- Monitor for unauthorized access attempts to management interfaces, especially around reboot events
🔍 How to Verify
Check if Vulnerable:
Check if device is Cisco Nexus 3550-F Switch with ACLs configured to block management interface traffic. Review ACL configuration with 'show running-config | include ip access-list' and 'show running-config interface management'.Check Version:
show version | include NXOSVerify Fix Applied:
Verify installed software version is listed as fixed in Cisco advisory using 'show version' command.📡 Detection & Monitoring
Log Indicators:
- Failed authentication attempts on management interface following reboots
- ACL deny counter increments for management interface rules
Network Indicators:
- Traffic to management interface IPs from unauthorized sources
- Port scans targeting management interfaces
SIEM Query:
source_ip IN [unauthorized_networks] AND dest_ip IN [switch_management_ips] AND event_time AROUND [reboot_times]