Unusual Process For a Linux Host

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Identifies rare processes that do not usually run on individual hosts, which can indicate execution of unauthorized services, malware, or persistence mechanisms. Processes are considered rare when they only run occasionally as compared with other processes running on the host.

Rule type: machine_learning

Machine learning job: v3_rare_process_by_host_linux

Machine learning anomaly threshold: 50

Severity: low

Risk score: 21

Runs every: 15 minutes

Searches indices from: now-45m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Elastic
  • Host
  • Linux
  • Threat Detection
  • ML
  • Persistence

Version: 100 (version history)

Added (Elastic Stack release): 7.7.0

Last modified (Elastic Stack release): 8.5.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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A newly installed program or one that runs rarely as part of a monthly or quarterly workflow could trigger this alert.

Investigation guide

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## Triage and analysis

### Investigating an Unusual Linux Process
Detection alerts from this rule indicate the presence of a Linux process that is rare and unusual for the host it ran on. Here are some possible avenues of investigation:
- Consider the user as identified by the username field. Is this program part of an expected workflow for the user who ran this program on this host?
- Examine the history of execution. If this process only manifested recently, it might be part of a new software package. If it has a consistent cadence (for example if it runs monthly or quarterly), it might be part of a monthly or quarterly business process.
- Examine the process arguments, title and working directory. These may provide indications as to the source of the program or the nature of the tasks it is performing.

Threat mapping

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Framework: MITRE ATT&CKTM

Rule version history

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Version 100 (8.5.0 release)
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Version 9 (8.4.0 release)
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Version 8 (8.3.0 release)
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Version 7 (7.15.0 release)
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Version 6 (7.14.0 release)
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Version 5 (7.13.0 release)
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Version 4 (7.12.0 release)
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Version 3 (7.10.0 release)
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Version 2 (7.9.0 release)
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