Name:Linux Binary Executed from Shared Memory Directory id:2e954190-d547-447c-94d7-d8acac97873b version:1 date:None author:Raven Tait, Splunk status:production type:Anomaly Description:The following analytic identifies the execution of a binary by root from Linux shared memory directories (/dev/shm/ and /run/shm/). Threat actors place executables in these directories to persist on high-uptime servers as system backdoors. Both /dev/shm and /run/shm are tmpfs-backed directories that exist only in virtual memory with no persistent storage, making them attractive for staging fileless or semi-fileless malware while avoiding disk forensics. Data_source:
-Sysmon for Linux EventID 1
search:| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime
from datamodel=Endpoint.Processes where
Processes.process_path IN ( "/dev/shm/*", "/run/shm/*" ) Processes.user=root
how_to_implement:The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint` data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process. known_false_positives:Legitimate applications may use shared memory directories for temporary file storage or inter-process communication. Verify any flagged activity against known software behavior and filter accordingly. References: -https://linuxsecurity.com/features/fileless-malware-on-linux -https://twitter.com/GossiTheDog/status/1522964028284411907 -https://github.com/elastic/detection-rules/blob/main/rules/linux/execution_process_started_in_shared_memory_directory.toml drilldown_searches: earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View the detection results for - "$user$" and "$dest$"' search:'%original_detection_search% | search user = "$user$" dest = "$dest$"' name:'View risk events for the last 7 days for - "$user$" and "$dest$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`' earliest_offset:'7d' latest_offset:'0' analytic_story:['Linux Post-Exploitation', 'Linux Persistence Techniques', 'Linux Privilege Escalation', 'Compromised Linux Host']
