LoFP LoFP / telnet can be used for both benign or malicious purposes. telnet is included by default in some linux distributions, so its presence is not inherently suspicious. the use of telnet to manage devices remotely has declined in recent years in favor of more secure protocols such as ssh. telnet usage by non-automated tools or frameworks may be suspicious.

Techniques

Sample rules

Connection to Internal Network via Telnet

Description

Telnet provides a command line interface for communication with a remote device or server. This rule identifies Telnet network connections to non-publicly routable IP addresses.

Detection logic

sequence by process.entity_id
  [process where host.os.type == "linux" and process.name == "telnet" and event.type == "start"]
  [network where host.os.type == "linux" and process.name == "telnet" and cidrmatch(
     destination.ip, "10.0.0.0/8", "127.0.0.0/8", "169.254.0.0/16", "172.16.0.0/12", "192.0.0.0/24", "192.0.0.0/29",
     "192.0.0.8/32", "192.0.0.9/32", "192.0.0.10/32", "192.0.0.170/32", "192.0.0.171/32", "192.0.2.0/24",
     "192.31.196.0/24", "192.52.193.0/24", "192.168.0.0/16", "192.88.99.0/24", "224.0.0.0/4", "100.64.0.0/10",
     "192.175.48.0/24", "198.18.0.0/15", "198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", "::1", "FE80::/10",
     "FF00::/8"
    )
  ]

Connection to External Network via Telnet

Description

Telnet provides a command line interface for communication with a remote device or server. This rule identifies Telnet network connections to publicly routable IP addresses.

Detection logic

sequence by process.entity_id
  [process where host.os.type == "linux" and process.name == "telnet" and event.type == "start"]
  [network where host.os.type == "linux" and process.name == "telnet" and not cidrmatch(
     destination.ip, "10.0.0.0/8", "127.0.0.0/8", "169.254.0.0/16", "172.16.0.0/12", "192.0.0.0/24", "192.0.0.0/29",
     "192.0.0.8/32", "192.0.0.9/32", "192.0.0.10/32", "192.0.0.170/32", "192.0.0.171/32", "192.0.2.0/24",
     "192.31.196.0/24", "192.52.193.0/24", "192.168.0.0/16", "192.88.99.0/24", "224.0.0.0/4", "100.64.0.0/10",
     "192.175.48.0/24", "198.18.0.0/15", "198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", "::1", "FE80::/10",
     "FF00::/8"
    )
  ]