[metadata]
creation_date = "2022/05/06"
maturity = "production"
updated_date = "2022/05/09"

[rule]
author = ["Elastic"]
description = """
Identifies Linux binary(s) abuse to breakout out of restricted shells or environments by spawning an interactive system
shell. The linux utility(s) activity of spawning shell is not a standard use of the binary for a user or system
administrator. It may indicates an attempt to improve the capabilities or stability of an adversary access.
"""
from = "now-9m"
index = ["logs-endpoint.events.*"]
language = "eql"
license = "Elastic License v2"
name = "Linux Restricted Shell Breakout via  Linux Binary(s)"
references = [
    "https://gtfobins.github.io/gtfobins/apt/",
    "https://gtfobins.github.io/gtfobins/apt-get/",
    "https://gtfobins.github.io/gtfobins/nawk/",
    "https://gtfobins.github.io/gtfobins/mawk/",
    "https://gtfobins.github.io/gtfobins/awk/",
    "https://gtfobins.github.io/gtfobins/gawk/",
    "https://gtfobins.github.io/gtfobins/busybox/",
    "https://gtfobins.github.io/gtfobins/c89/",
    "https://gtfobins.github.io/gtfobins/c99/",
    "https://gtfobins.github.io/gtfobins/cpulimit/",
    "https://gtfobins.github.io/gtfobins/crash/",
    "https://gtfobins.github.io/gtfobins/env/",
    "https://gtfobins.github.io/gtfobins/expect/",
    "https://gtfobins.github.io/gtfobins/find/",
    "https://gtfobins.github.io/gtfobins/flock/",
    "https://gtfobins.github.io/gtfobins/gcc/",
    "https://gtfobins.github.io/gtfobins/mysql/",
    "https://gtfobins.github.io/gtfobins/nice/",
    "https://gtfobins.github.io/gtfobins/ssh/",
    "https://gtfobins.github.io/gtfobins/vi/",
    "https://gtfobins.github.io/gtfobins/vim/",
    "https://gtfobins.github.io/gtfobins/capsh/",
    "https://gtfobins.github.io/gtfobins/byebug/",
]
risk_score = 47
rule_id = "52376a86-ee86-4967-97ae-1a05f55816f0"
severity = "medium"
tags = ["Elastic", "Host", "Linux", "Threat Detection", "Execution", "GTFOBins"]
timestamp_override = "event.ingested"
type = "eql"

query = '''
process where event.type == "start" and

  /* 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 == "byebug") 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 == "/")
    ) 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(*)}")
'''


[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1059"
name = "Command and Scripting Interpreter"
reference = "https://attack.mitre.org/techniques/T1059/"
[[rule.threat.technique.subtechnique]]
id = "T1059.004"
name = "Unix Shell"
reference = "https://attack.mitre.org/techniques/T1059/004/"



[rule.threat.tactic]
id = "TA0002"
name = "Execution"
reference = "https://attack.mitre.org/tactics/TA0002/"