Potential Linux SSH Brute Force Detected

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Identifies multiple consecutive login failures targeting an user account from the same source address and within a short time interval. Adversaries will often brute force login attempts across multiple users with a common or known password, in an attempt to gain access to accounts.

Rule type: eql

Rule indices:

  • auditbeat-*
  • logs-system.auth-*

Severity: medium

Risk score: 47

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

Tags:

  • Elastic
  • Host
  • Linux
  • Threat Detection
  • Credential Access

Version: 1

Added (Elastic Stack release): 8.5.0

Rule authors: Elastic

Rule license: Elastic License v2

Investigation guide

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## Triage and analysis

### Investigating Potential SSH Brute Force Attack

The rule identifies consecutive SSH login failures targeting a user account from the same source IP address to the
same target host indicating brute force login attempts.

#### Possible investigation steps

- Investigate the login failure user name(s).
- Investigate the source IP address of the failed ssh login attempt(s).
- Investigate other alerts associated with the user/host during the past 48 hours.
- Identify the source and the target computer and their roles in the IT environment.

### False positive analysis

- Authentication misconfiguration or obsolete credentials.
- Service account password expired.
- Infrastructure or availability issue.

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved hosts to prevent further post-compromise behavior.
- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
identified.
- Reset passwords for these accounts and other potentially compromised credentials.
- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
malware components.
- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
mean time to respond (MTTR).

Rule query

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sequence by host.id, source.ip, user.name with maxspan=10s
[authentication where event.action in ("ssh_login", "user_login") and
event.outcome == "failure" and source.ip != null and source.ip !=
"0.0.0.0" and source.ip != "::" ] with runs=10

Threat mapping

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Framework: MITRE ATT&CKTM