[metadata] creation_date = "2022/05/06" maturity = "production" updated_date = "2022/05/25" [rule] author = ["Elastic"] description = """ Identifies Linux binary(s) abuse to breakout 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)" note = """## Triage and analysis ### Investigating Shell Evasion via Linux Utilities Detection alerts from this rule indicate that a Linux utility has been abused to breakout of restricted shells or environments by spawning an interactive system shell. Here are some possible avenues of investigation: - Examine the entry point to the host and user in action via the Analyse View. - Identify the session entry leader and session user - Examine the contents of session leading to the abuse via the Session View. - Examine the command execution pattern in the session, which may lead to suspricous activities - Examine the execution of commands in the spawned shell. - Identify imment threat to the system from the executed commands - Take necessary incident response actions to contain any malicious behviour caused via this execution. ### Related rules - A malicious spawned shell can execute any of the possible MITTRE ATT&CK vectors mainly to impair defences. - Hence its adviced to enable defence evasion and privilige escalation rules accordingly in your environment ### Response and remediation Initiate the incident response process based on the outcome of the triage. - If the triage releaved suspicious netwrok activity from the malicious spawned shell, - Isolate the involved host to prevent further post-compromise behavior. - If the triage identified malware execution via the maliciously spawned shell, - Search the environment for additional compromised hosts. - Implement temporary network rules, procedures, and segmentation to contain the malware. - Stop suspicious processes. - Immediately block the identified indicators of compromise (IoCs). - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system. - If the triage revelaed defence evasion for imparing defenses - Isolate the involved host to prevent further post-compromise behavior. - Identified the disabled security guard components on the host and take necessary steps in renebaling the same. - If any tools have been disbaled / uninstalled or config tampered work towards reenabling the same. - If the triage revelaed addition of persistence mechanism exploit like auto start scripts - Isolate further login to the systems that can initae auto start scripts. - Identify the auto start scripts and disable and remove the same from the systems - If the triage revealed data crawling or data export via remote copy - Investigate credential exposure on systems compromised / used / decoded by the attacker during the data crawling - Intiate compromised credential deactivation and credential rotation process for all exposed crednetials. - Investiagte if any IPR data was accessed during the data crawling and take appropriate actions. - Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector. - Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the mean time to respond (MTTR). ## Config The session view analysis for the command alerted is avalible in versions 8.2 and above. """ 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/", "https://gtfobins.github.io/gtfobins/git/", ] 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 in ("byebug","git")) 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/"