PH_Rule_TH_Linux_9
Enabled
Detects attempts to delete files via shred command. Malware or other files dropped or created on a system by an adversary may leave traces behind as to what was done within a network and how. Adversaries may remove these files over the course of an intrusion to keep their footprint low or remove them at the end as part of the post-intrusion cleanup process. This requires process monitoring via FortiSIEM Linux agent.
9
Security
Defense Evasion
Defense Evasion consists of techniques that adversaries use to avoid detection throughout their compromise. Techniques used for defense evasion include uninstalling/disabling security software or obfuscating/encrypting data and scripts. Adversaries also leverage and abuse trusted processes to hide and masquerade their malware. Other tactics’ techniques are cross-listed here when those techniques include the added benefit of subverting defenses.
https://attack.mitre.org/tactics/TA0005T1070.004
Indicator Removal on Host: File Deletion
Adversaries may delete files left behind by the actions of their intrusion activity to minimize the adversary's footprint. Tools such as cmd functions such as DEL, secure deletion tools such as Windows Sysinternals SDelete, or other third-party file deletion tools can be used.
https://attack.mitre.org/techniques/T1070/004Server
Linux Process Monitoring via FortiSIEM Agent
Correlation
No remediation guidance specified
If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.
300 seconds
If the following defined pattern/s occur within a 300 second time window.
Filter
This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.
This is the query logic that matches incoming events
eventType = "LINUX_PROCESS_EXEC" AND procName = "shred" AND swParam REGEXP (".*-u.*|.*--remove.*|.*-z.*|.*--zero.*")
This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID
hostName, user, procName, swParam
This is most typically a numerical constraint that defines when the rule should trigger an incident
COUNT(*) >= 1
This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.
The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern
hostName = Filter.hostName,
user = Filter.user,
procName = Filter.procName,
swParam = Filter.swParam