Elastic Security Detection Rules

Accepted Default Telnet Port Connection

Last updated a month ago on 2026-06-08
Created 6 years ago on 2020-02-18

About

This rule detects network events that may indicate the use of Telnet traffic. Telnet is commonly used by system administrators to remotely control older or embedded systems using the command line shell. It should almost never be directly exposed to the Internet, as it is frequently targeted and exploited by threat actors as an initial access or backdoor vector. As a plain-text protocol, it may also expose usernames and passwords to anyone capable of observing the traffic.
Tags
Domain: EndpointUse Case: Threat DetectionTactic: Command and ControlTactic: Lateral MovementTactic: Initial AccessData Source: FortinetData Source: PAN-OSData Source: pfSenseData Source: SonicWallData Source: SuricataLanguage: kuery
Severity
medium
Risk Score
47
MITRE ATT&CK™

Command and Control (TA0011)(external, opens in a new tab or window)

↳ Application Layer Protocol (T1071)(external, opens in a new tab or window)

Lateral Movement (TA0008)(external, opens in a new tab or window)

↳ Remote Services (T1021)(external, opens in a new tab or window)

Initial Access (TA0001)(external, opens in a new tab or window)

↳ External Remote Services (T1133)(external, opens in a new tab or window)

↳ Exploit Public-Facing Application (T1190)(external, opens in a new tab or window)

False Positive Examples
IoT (Internet of Things) devices and networks may use telnet and can be excluded if desired. Some business work-flows may use Telnet for administration of older devices. These often have a predictable behavior. Telnet activity involving an unusual source or destination may be more suspicious. Telnet activity involving a production server that has no known associated Telnet work-flow or business requirement is often suspicious.
License
Elastic License v2(external, opens in a new tab or window)

Definition

Rule Type
Query (Kibana Query Language)
Integration Pack
Prebuilt Security Detection Rules
Index Patterns
packetbeat-*auditbeat-*filebeat-*logs-network_traffic.*logs-panw.panos*logs-fortinet_fortigate.log-*logs-pfsense.log-*logs-sonicwall_firewall.log-*logs-suricata.*
Related Integrations

network_traffic(external, opens in a new tab or window)

panw(external, opens in a new tab or window)

fortinet_fortigate(external, opens in a new tab or window)

pfsense(external, opens in a new tab or window)

sonicwall_firewall(external, opens in a new tab or window)

suricata(external, opens in a new tab or window)

Query
text code block:
(data_stream.dataset:(fortinet_fortigate.log or network_traffic.flow
        or panw.panos or pfsense.log or sonicwall_firewall.log or suricata.eve)
    or event.category:(network or network_traffic))
    and event.type:(connection and not (denied or end))
    and not event.action:(Reject or client-rst or connection-denied or
        connection-end or denied or deny or flow_denied or flow_dropped or
        flow_terminated or network_flow or server-rst or timeout)
    and not (event.action:netflow_flow and not network.packets > 1)
    and not network.application:(stretchoid-scanning or traceroute)
    and destination.port:23

Install detection rules in Elastic Security

Detect Accepted Default Telnet Port Connection in the Elastic Security detection engine by installing this rule into your Elastic Stack.

To setup this rule, check out the installation guide for Prebuilt Security Detection Rules(external, opens in a new tab or window).