CVE-2025-20311
📋 TL;DR
An unauthenticated attacker on the same network segment can send specially crafted Ethernet frames to Cisco Catalyst 9000 switches running vulnerable IOS XE software, causing specific egress ports to drop all traffic and creating a denial-of-service condition. This affects organizations using these switches in their network infrastructure.
💻 Affected Systems
- Cisco Catalyst 9000 Series 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
Critical network segments become unavailable as multiple ports drop all traffic, disrupting business operations and connectivity.
Likely Case
Targeted DoS attacks against specific ports causing localized network outages.
If Mitigated
Limited impact due to network segmentation and proper access controls preventing adjacent attacker access.
🎯 Exploit Status
Exploitation requires sending crafted Ethernet frames, which is relatively straightforward for network-aware attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Cisco Security Advisory for specific fixed versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-cat9k-PtmD7bgy
Restart Required: Yes
Instructions:
1. Review Cisco advisory for affected versions. 2. Download and install the fixed IOS XE software version. 3. Schedule maintenance window for switch reboot. 4. Verify patch installation and functionality.
🔧 Temporary Workarounds
Network Segmentation
allImplement strict network segmentation to limit adjacent attacker access to vulnerable switches
Access Control Lists
allApply ACLs to restrict traffic to trusted sources only
access-list 100 permit ip trusted-network any
interface gigabitethernet1/0/1
ip access-group 100 in
🧯 If You Can't Patch
- Implement strict network segmentation and VLAN isolation
- Deploy intrusion detection/prevention systems to monitor for crafted Ethernet frames
🔍 How to Verify
Check if Vulnerable:
Check IOS XE version on Catalyst 9000 switches and compare with affected versions in Cisco advisoryCheck Version:
show version | include VersionVerify Fix Applied:
Verify installed IOS XE version matches or exceeds fixed versions listed in Cisco advisory📡 Detection & Monitoring
Log Indicators:
- Increased port error counters
- Interface state changes to err-disable
- Traffic drop alerts
Network Indicators:
- Unusual Ethernet frame patterns
- Sudden traffic drops on specific ports
- Port flapping events
SIEM Query:
source="catalyst-switch" ("err-disable" OR "dropped" OR "storm-control")