Rule tuning as part of Linux Detection Rules Review (#2210)

rules/linux/execution_shell_evasion_linux_binary.toml

@@ -1,7 +1,7 @@
 [metadata]
 creation_date = "2022/05/06"
 maturity = "production"
-updated_date = "2022/07/28"
+updated_date = "2022/08/01"
 
 [rule]
 author = ["Elastic"]
@@ -103,37 +103,39 @@ type = "eql"
 query = '''
 process where event.type == "start" and
 
-  /* launch shells from unusual process */
-  (process.name == "capsh" and process.args == "--") or
+    /* launch shells from unusual process */
+    (process.name == "capsh" and process.args == "--") or
 
-  /* launching shells from unusual parents or parent+arg combos */
-  (process.name in ("bash", "sh", "dash","ash") and
-    (process.parent.name in ("byebug","git","ftp","strace")) or
+    /* launching shells from unusual parents or parent+arg combos */
+    (process.name in ("bash", "sh", "dash","ash") and
+        (process.parent.name in ("byebug","git","ftp","strace")) or
 
-    /* shells specified in parent args */
-    /* nice rule is broken in 8.2 */
-    (process.parent.args in ("/bin/sh", "/bin/bash", "/bin/dash", "/bin/ash", "sh", "bash", "dash", "ash") and
-        (process.parent.name == "nice") or
-        (process.parent.name == "cpulimit" and process.parent.args == "-f") or
-        (process.parent.name == "find" and process.parent.args == "-exec" and process.parent.args == ";") or
-        (process.parent.name == "flock" and process.parent.args == "-u" and process.parent.args == "/")
+        /* shells specified in parent args */
+        /* nice rule is broken in 8.2 */
+        (process.parent.args in ("/bin/sh", "/bin/bash", "/bin/dash", "/bin/ash", "sh", "bash", "dash", "ash") and
+            (
+             (process.parent.name == "nice") or
+             (process.parent.name == "cpulimit" and process.parent.args == "-f") or
+             (process.parent.name == "find" and process.parent.args == "-exec" and process.parent.args == ";") or
+             (process.parent.name == "flock" and process.parent.args == "-u" and process.parent.args == "/")
+            )
+        ) or
+
+         /* shells specified in args */
+         (process.args in ("/bin/sh", "/bin/bash", "/bin/dash", "/bin/ash", "sh", "bash", "dash", "ash") and
+            (process.parent.name == "crash" and process.parent.args == "-h") or
+            (process.name == "sensible-pager" and process.parent.name in ("apt", "apt-get") and process.parent.args == "changelog")
+            /* scope to include more sensible-pager invoked shells with different parent process to reduce noise and remove false positives */
+          )
     ) or
-
-    /* shells specified in args */
-    (process.args in ("/bin/sh", "/bin/bash", "/bin/dash", "/bin/ash", "sh", "bash", "dash", "ash") and
-        (process.parent.name == "crash" and process.parent.args == "-h") or
-        (process.name == "sensible-pager" and process.parent.name in ("apt", "apt-get") and process.parent.args == "changelog")
-        /* scope to include more sensible-pager invoked shells with different parent process to reduce noise and remove false positives */
-    )
-  ) or
-  (process.name == "busybox" and process.args_count == 2 and process.args in ("/bin/sh", "/bin/bash", "/bin/dash", "/bin/ash", "sh", "bash", "dash", "ash") )or
-  (process.name == "env" and process.args_count == 2 and process.args in ("/bin/sh", "/bin/bash", "/bin/dash", "/bin/ash", "sh", "bash", "dash", "ash")) or
-  (process.parent.name in ("vi", "vim") and process.parent.args == "-c" and process.parent.args in (":!/bin/bash", ":!/bin/sh", ":!bash", ":!sh")) or
-  (process.parent.name in ("c89","c99", "gcc") and process.parent.args in ("sh,-s", "bash,-s", "dash,-s", "ash,-s", "/bin/sh,-s", "/bin/bash,-s", "/bin/dash,-s", "/bin/ash,-s") and process.parent.args == "-wrapper") or
-  (process.parent.name == "expect" and process.parent.args == "-c" and process.parent.args in ("spawn /bin/sh;interact", "spawn /bin/bash;interact", "spawn /bin/dash;interact", "spawn sh;interact", "spawn bash;interact", "spawn dash;interact")) or
-  (process.parent.name == "mysql" and process.parent.args == "-e" and process.parent.args in ("\\!*sh", "\\!*bash", "\\!*dash", "\\!*/bin/sh", "\\!*/bin/bash", "\\!*/bin/dash")) or
-  (process.parent.name == "ssh" and process.parent.args == "-o" and process.parent.args in ("ProxyCommand=;sh 0<&2 1>&2", "ProxyCommand=;bash 0<&2 1>&2", "ProxyCommand=;dash 0<&2 1>&2", "ProxyCommand=;/bin/sh 0<&2 1>&2", "ProxyCommand=;/bin/bash 0<&2 1>&2", "ProxyCommand=;/bin/dash 0<&2 1>&2")) or
-  (process.parent.name in ("nawk", "mawk", "awk", "gawk") and process.parent.args : "BEGIN {system(*)}")
+    (process.name == "busybox" and process.args_count == 2 and process.args in ("/bin/sh", "/bin/bash", "/bin/dash", "/bin/ash", "sh", "bash", "dash", "ash") )or
+    (process.name == "env" and process.args_count == 2 and process.args in ("/bin/sh", "/bin/bash", "/bin/dash", "/bin/ash", "sh", "bash", "dash", "ash")) or
+    (process.parent.name in ("vi", "vim") and process.parent.args == "-c" and process.parent.args in (":!/bin/bash", ":!/bin/sh", ":!bash", ":!sh")) or
+    (process.parent.name in ("c89","c99", "gcc") and process.parent.args in ("sh,-s", "bash,-s", "dash,-s", "ash,-s", "/bin/sh,-s", "/bin/bash,-s", "/bin/dash,-s", "/bin/ash,-s") and process.parent.args == "-wrapper") or
+    (process.parent.name == "expect" and process.parent.args == "-c" and process.parent.args in ("spawn /bin/sh;interact", "spawn /bin/bash;interact", "spawn /bin/dash;interact", "spawn sh;interact", "spawn bash;interact", "spawn dash;interact")) or
+    (process.parent.name == "mysql" and process.parent.args == "-e" and process.parent.args in ("\\!*sh", "\\!*bash", "\\!*dash", "\\!*/bin/sh", "\\!*/bin/bash", "\\!*/bin/dash")) or
+    (process.parent.name == "ssh" and process.parent.args == "-o" and process.parent.args in ("ProxyCommand=;sh 0<&2 1>&2", "ProxyCommand=;bash 0<&2 1>&2", "ProxyCommand=;dash 0<&2 1>&2", "ProxyCommand=;/bin/sh 0<&2 1>&2", "ProxyCommand=;/bin/bash 0<&2 1>&2", "ProxyCommand=;/bin/dash 0<&2 1>&2")) or
+    (process.parent.name in ("nawk", "mawk", "awk", "gawk") and process.parent.args : "BEGIN {system(*)}")
 '''