What if the very protocol used to manage and monitor your network's core infrastructure could be used to crash it or, even worse handover complete control to an attacker?
The recent disclosed vulnerability (CVE-2024-20376) in the SNMP (Simple Network Management Protocol) subsystem of Cisco IOS and IOS XE Software does exactly that. This flaw is a double-edged sword, allowing a remote, unauthenticated attacker to either launch a devastating Denial-of-Service (DoS) attack or achieve the ultimate prize full Remote Code Execution (RCE).
Given that Cisco devices form the backbone of countless global enterprises and service providers, this vulnerability poses a severe risk to network stability and security
The Vulnerability Demystified
What is SNMP?
SNMP (SimpleNetwork Management Protocol) is a standard protocol used to monitor and manage devices like routers, switches, firewalls, and servers. It works by exchanging messages (SNMP packets) between network devices and management systems, acting as the “language” they use to communicate.
Why It’s Critical
- SNMP is often enabled by default or used for network monitoring and management; vulnerable devices are internet-facing or reachable from internal networks
- Exploiting SNMP is attractive to attackers because it’s a standard protocol with broad reach across network infrastructure
- A successful exploit could let adversaries disrupt network infrastructure or use the device as a foothold for lateral movement
Affected Products
As published by CISCO, This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco IOS Software or CiscoIOS XE Software.
Meraki MS390 and Cisco Catalyst 9300 Series Switches that are running Meraki CS 17 and earlier are also affected. This is fixed in CiscoIOS XE Software Release 17.15.4a.
Note: This vulnerability affects all versions of SNMP. All devices that have SNMP enabled and have not explicitly excluded the affected object ID (OID) should be considered vulnerable.
Cisco has confirmed that this vulnerability does not affect the following Cisco products
- IOS XR Software
- NX-OS Software
To determine if a device has SNMPv1 or v2c enabled, use the show running-config | include snmp-server community CLI command. If there is output, SNMP is enabled, as shown in the following example:
Router# show running-config | include snmp-server community
snmp-server community public ro
To determine whether a device has SNMPv3 enabled, use the show running-config | include snmp-server group and show snmp user CLI commands. If there is output from both commands, SNMPv3 is enabled, as shown in the following example:
Router# show running-config | include snmp-servergroup
snmp-server group v3group v3 noauth
Router# show snmp user
User name: remoteuser1
Engine ID: 800000090300EE01E71C178C
storage-type: nonvolatile active
Authentication Protocol: SHA
Privacy Protocol: None
Group-name: v3group
Mitigation
- Apply Patches Immediately – Update affected Cisco IOS / IOS XE devices with the fixes provided in Cisco’s advisory.
- Disable SNMP if Unused – If SNMP is not required, disable it entirely.
- Restrict SNMP Access – Limit SNMP to trusted management networks; block from untrusted or internet-facing segments.
- Use Strong Community Strings / SNMPv3 – Use SNMPv3 with authentication and encryption, and avoid default community strings.
- Monitor SNMP Traffic – Deploy detection rules for anomalous SNMP queries or malformed SNMP packets.
- Network Segmentation – Segregate management traffic and isolate infrastructure devices from user networks.
To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides the Cisco Software Checker.
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