Simple Network Management Protocol (SNMP) is a UDP service that runs on port 161/UDP. It is used for network management purposes and should be reachable only from known locations using secure channels.

I reviewed my honeypot today for interesting connections during december 2019. Saw an increase of snmp queries with the following distribution:

This is interesting as attackers are querying for the Community-Based Simple Network Management Protocol version 2 (SNMPv2c) instead of SNMPv2. It introduced GetBulkRequest command to gather large amount of data. SNMPv2c includes SNMPv2 without the SNMPv2 security model, using instead the simple community-based security scheme of SNMPv1.

Our ISC data shows this port was also active during december with a small spike during the first week of 2020:

Shodan report shows many devices connected to the internet with open SNMP port:

And there are domains with an important number of devices with open SNMP port. Source is Shodan:

We can conclude the following:

• There are devices that still have SNMP open to the Internet and the attackers know it. They predominantly search for devices that respond under the SNMPv2c protocol.
• You should not place devices on the Internet with open SNMP services. This is a very cheap way for an attacker to gather intelligence about your network and traffic.
• Please always use secure protocols:
  • SNMPv1 send passwords in clear text. SNMPv2 is prone to password hashing attacks.
  • SNMPv1 and SNMPv2 are vulnerable to IP spoofing. None of them should be used. 
  • SNMPv3 is vulnerable to brute force and dictionary attacks. This is the current protocol version. To mitigate the vulnerabilities, you should use IPSec transport connections.

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Manuel Humberto Santander Pelaez
SANS Internet Storm Center - Handler
Twitter:@manuelsantander
Web:http://manuel.santander.name
e-mail: msantand at isc dot sans dot org