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SNMP: Spike in Brute-force Attempts Recently Observed

Simple Network Monitoring Protocol (SNMP) has been widely deployed as an important network management tool for decades, is a key component of scalable network device management, and is configurable in nearly all network infrastructure devices sold today. As with any management protocol, if not configured securely, it can be leveraged as an opening for attackers to gain access to the network and begin reconnaissance of network infrastructure. In the worst case, if read-write community strings are weak or not properly protected, attackers could directly manipulate device configurations.

Cisco has recently seen a spike in brute-force attempts to access networking devices configured for SNMP using the standard ports (UDP ports 161 and 162). Attacks we’ve observed have been going after well known SNMP community strings and are focused on network edge devices. We have been working with our Technical Assistance Center (TAC) to assist customers in mitigating any problems caused by the brute-force attempts.

While there’s nothing new about brute-force attacks against network devices, in light of these recent findings, customers may want to revisit their SNMP configurations and ensure they follow security best practices, including using strong passwords and community strings and using ACLs to restrict access to trusted network management endpoints.

Cisco has published a number of best practices documents for securing the management plane, including SNMP configuration:

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Miscreants and the Principle of Least Effort

Back in the old days, when security was much more of an afterthought, it was obvious that miscreants were familiar with the principle of least effort. Information security was still in its Wild West days. Managed disclosure and patching did not really exist. Most companies were just coming to realize they would need to put some effort into securing their assets. I was tasked with most of the security deployments and forensic investigation at a startup hosting company. We had a lot of bandwidth (at the time) and a lot of poorly managed servers. You could watch our gateway and know when a new vulnerability was discovered in the underground. You could see miscreants scanning for a specific service in a specific network. Miscreants had done their homework, and knew where the vulnerable hosts resided. This targeting was efficient. Sure enough, hosts would start being compromised and a few days later some sort of official disclosure would happen detailing the vulnerability the miscreants had been scanning for. Read More »

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