CVE-2025-20151
📋 TL;DR
This vulnerability allows authenticated SNMPv3 users to poll Cisco IOS/IOS XE devices even when their access should be denied by configuration. The flaw occurs because SNMPv3 configuration persists incorrectly in startup configs after removal. Only devices running affected Cisco software with SNMPv3 enabled are vulnerable.
💻 Affected Systems
- Cisco IOS Software
- Cisco IOS XE Software
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers with valid SNMPv3 credentials could perform unauthorized SNMP operations, potentially gathering sensitive device information or configuration details that should be restricted.
Likely Case
Authorized users whose access should have been revoked can continue performing SNMP queries, potentially accessing information they should no longer have permission to view.
If Mitigated
With proper network segmentation and SNMP community string security, impact is limited to information disclosure from devices that should have denied access.
🎯 Exploit Status
Exploitation requires valid SNMPv3 user credentials. Attacker cannot modify SNMPv3 configuration, only leverage existing access that should have been denied.
🛠️ 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-snmpv3-qKEYvzsy
Restart Required: Yes
Instructions:
1. Review Cisco advisory for affected versions. 2. Upgrade to fixed software release. 3. Reload device to apply new configuration. 4. Verify SNMPv3 access controls are functioning correctly.
🔧 Temporary Workarounds
Disable SNMPv3
allCompletely disable SNMPv3 if not required for operations
no snmp-server group <groupname> v3
no snmp-server user <username> <groupname> v3
Implement ACL-based SNMP restrictions
allUse access control lists to restrict SNMP access at network level
access-list 10 permit <authorized_hosts>
snmp-server community <string> ro 10
🧯 If You Can't Patch
- Implement strict network ACLs to limit SNMP access to trusted management stations only
- Regularly rotate SNMPv3 credentials and verify removed users cannot access devices
🔍 How to Verify
Check if Vulnerable:
Check if device runs affected Cisco IOS/IOS XE version and has SNMPv3 configured. Test if removed SNMPv3 users can still poll device.Check Version:
show version | include VersionVerify Fix Applied:
After patching, verify removed SNMPv3 users cannot access device. Test SNMP polling from unauthorized sources.📡 Detection & Monitoring
Log Indicators:
- SNMP authentication failures from previously authorized users
- SNMP requests from IPs not in allowed ACLs
Network Indicators:
- SNMPv3 traffic from unexpected sources
- SNMP polling patterns inconsistent with authorized users
SIEM Query:
source="network_device" (protocol="SNMP" AND (user="removed_user" OR src_ip NOT IN allowed_ips))