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85 lines
4.2 KiB
YAML
85 lines
4.2 KiB
YAML
name: Linux SSH Authorized Keys Modification
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id: f5ab595e-28e5-4327-8077-5008ba97c850
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version: 6
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date: '2024-11-13'
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author: Michael Haag, Splunk
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status: production
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type: Anomaly
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description: The following analytic detects the modification of SSH Authorized Keys
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on Linux systems. It leverages process execution data from Endpoint Detection and
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Response (EDR) agents, specifically monitoring commands like "bash" and "cat" interacting
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with "authorized_keys" files. This activity is significant as adversaries often
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modify SSH Authorized Keys to establish persistent access to compromised endpoints.
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If confirmed malicious, this behavior could allow attackers to maintain unauthorized
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access, bypassing traditional authentication mechanisms and potentially leading
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to further exploitation or data exfiltration.
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data_source:
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- Sysmon for Linux EventID 1
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search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
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as lastTime from datamodel=Endpoint.Processes where Processes.process_name IN ("bash","cat")
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Processes.process IN ("*/authorized_keys*") by Processes.dest Processes.user Processes.parent_process_name
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Processes.process_name Processes.process Processes.process_id Processes.parent_process_id
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| `drop_dm_object_name(Processes)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`
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| `linux_ssh_authorized_keys_modification_filter`'
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how_to_implement: The detection is based on data that originates from Endpoint Detection
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and Response (EDR) agents. These agents are designed to provide security-related
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telemetry from the endpoints where the agent is installed. To implement this search,
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you must ingest logs that contain the process GUID, process name, and parent process.
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Additionally, you must ingest complete command-line executions. These logs must
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be processed using the appropriate Splunk Technology Add-ons that are specific to
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the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint`
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data model. Use the Splunk Common Information Model (CIM) to normalize the field
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names and speed up the data modeling process.
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known_false_positives: Filtering will be required as system administrators will add
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and remove. One way to filter query is to add "echo".
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references:
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- https://redcanary.com/blog/lateral-movement-with-secure-shell/
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- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1098.004/T1098.004.md
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drilldown_searches:
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- name: View the detection results for - "$user$" and "$dest$"
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search: '%original_detection_search% | search user = "$user$" dest = "$dest$"'
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earliest_offset: $info_min_time$
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latest_offset: $info_max_time$
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- name: View risk events for the last 7 days for - "$user$" and "$dest$"
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search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$",
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"$dest$") starthoursago=168 | stats count min(_time) as firstTime max(_time)
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as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk
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Message" values(analyticstories) as "Analytic Stories" values(annotations._all)
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as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics"
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by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
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earliest_offset: $info_min_time$
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latest_offset: $info_max_time$
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rba:
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message: An instance of $parent_process_name$ spawning $process_name$ was identified
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on endpoint $dest$ by user $user$ modifying SSH Authorized Keys.
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risk_objects:
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- field: user
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type: user
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score: 15
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- field: dest
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type: system
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score: 15
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threat_objects:
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- field: parent_process_name
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type: parent_process_name
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- field: process_name
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type: process_name
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tags:
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analytic_story:
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- Linux Living Off The Land
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asset_type: Endpoint
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mitre_attack_id:
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- T1098.004
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product:
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- Splunk Enterprise
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- Splunk Enterprise Security
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- Splunk Cloud
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security_domain: endpoint
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tests:
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- name: True Positive Test
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attack_data:
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- data:
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https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1098.004/ssh_authorized_keys/authkey_linux-sysmon.log
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source: Syslog:Linux-Sysmon/Operational
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sourcetype: sysmon:linux
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