[New Rule] Suspicious Kernel Feature Activity (#4676)

rules/linux/defense_evasion_sysctl_kernel_feature_activity.toml

@@ -0,0 +1,90 @@
+[metadata]
+creation_date = "2025/04/29"
+integration = ["endpoint"]
+maturity = "production"
+updated_date = "2025/04/29"
+
+[rule]
+author = ["Elastic"]
+description = """
+This rule detects the modification and reading of kernel features through built-in commands. Attackers may collect
+information, disable or weaken Linux kernel protections. For example, an attacker may modify ASLR protection by
+disabling kernel.randomize_va_space, allow ptrace by setting kernel.yama.ptrace_scope to 0, or disable the
+NMI watchdog by setting kernel.nmi_watchdog to 0. These changes may be used to impair defenses and evade detection.
+"""
+from = "now-9m"
+index = [
+    "logs-endpoint.events.process*",
+]
+language = "eql"
+license = "Elastic License v2"
+name = "Suspicious Kernel Feature Activity"
+risk_score = 21
+rule_id = "3aff6ab1-18bd-427e-9d4c-c5732110c261"
+severity = "low"
+tags = [
+    "Domain: Endpoint",
+    "OS: Linux",
+    "Use Case: Threat Detection",
+    "Tactic: Defense Evasion",
+    "Tactic: Discovery",
+    "Data Source: Elastic Defend",
+]
+timestamp_override = "event.ingested"
+type = "eql"
+query = '''
+process where host.os.type == "linux" and event.type == "start" and event.action == "exec" and
+process.command_line : (
+  "*/etc/sysctl.conf*", "*/etc/sysctl.d/*", "*/proc/sys/kernel/nmi_watchdog*",
+  "*/proc/sys/vm/nr_hugepages*", "*/proc/sys/kernel/yama/ptrace_scope*",
+  "*/proc/sys/kernel/randomize_va_space*", "*/proc/sys/vm/drop_caches*",
+  "*/proc/sys/kernel/sysrq*", "*grsecurity*", "*exec-shield*",
+  "*kernel.randomize_va_space*", "*kernel.yama.ptrace_scope*",
+  "*kernel.nmi_watchdog*", "*vm.nr_hugepages*", "*vm.drop_caches*",
+  "*kernel.sysrq*"
+) and
+process.parent.executable != null and 
+(
+  (process.name == "tee" and process.args like "-*a*") or // also detects --append
+  (process.name == "cat" and not process.parent.name in ("bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh", "fish")) or
+  (process.name == "grep" and process.args_count == 3 and not process.parent.name in ("bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh", "fish")) or
+  (process.name == "sysctl" and process.args like ("*-w*", "*--write*", "*=*")) or
+  (process.name in ("bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh", "fish") and process.args == "-c" and process.args : "*echo *")
+)
+'''
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+
+[rule.threat.tactic]
+name = "Defense Evasion"
+id = "TA0005"
+reference = "https://attack.mitre.org/tactics/TA0005/"
+
+[[rule.threat.technique]]
+name = "Impair Defenses"
+id = "T1562"
+reference = "https://attack.mitre.org/techniques/T1562/"
+
+[[rule.threat.technique.subtechnique]]
+name = "Indicator Blocking"
+id = "T1562.006"
+reference = "https://attack.mitre.org/techniques/T1562/006/"
+
+[[rule.threat.technique]]
+name = "Subvert Trust Controls"
+id = "T1553"
+reference = "https://attack.mitre.org/techniques/T1553/"
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+
+[[rule.threat.technique]]
+id = "T1082"
+name = "System Information Discovery"
+reference = "https://attack.mitre.org/techniques/T1082/"
+
+[rule.threat.tactic]
+id = "TA0007"
+name = "Discovery"
+reference = "https://attack.mitre.org/tactics/TA0007/"