[metadata] creation_date = "2022/05/06" integration = ["endpoint"] maturity = "production" min_stack_comments = "New fields added: required_fields, related_integrations, setup" min_stack_version = "8.3.0" updated_date = "2023/09/05" [rule] author = ["Elastic"] description = """ Identifies the abuse of a Linux binary to break out of a restricted shell or environment by spawning an interactive system shell. The activity of spawning a shell from a binary is not common behavior for a user or system administrator, and may indicate an attempt to evade detection, increase capabilities or enhance the stability of an adversary. """ 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). ## Setup 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/", "https://gtfobins.github.io/gtfobins/ftp/", ] risk_score = 47 rule_id = "52376a86-ee86-4967-97ae-1a05f55816f0" severity = "medium" tags = ["Domain: Endpoint", "OS: Linux", "Use Case: Threat Detection", "Tactic: Execution", "Data Source: Elastic Endgame", "Data Source: Elastic Defend"] timestamp_override = "event.ingested" type = "eql" query = ''' process where host.os.type == "linux" and event.type == "start" and ( /* launching shell from capsh */ (process.name == "capsh" and process.args == "--") or /* launching shells from unusual parents or parent+arg combos */ (process.name : "*sh" and ( (process.parent.name : "*awk" and process.parent.args : "BEGIN {system(*)}") or (process.parent.name == "git" and process.parent.args : ("*PAGER*", "!*sh", "exec *sh") or process.args : ("*PAGER*", "!*sh", "exec *sh") and not process.name == "ssh" ) or (process.parent.name : ("byebug", "ftp", "strace", "zip", "tar") and ( process.parent.args : "BEGIN {system(*)}" or (process.parent.args : ("*PAGER*", "!*sh", "exec *sh") or process.args : ("*PAGER*", "!*sh", "exec *sh")) or ( (process.parent.args : "exec=*sh" or (process.parent.args : "-I" and process.parent.args : "*sh")) or (process.args : "exec=*sh" or (process.args : "-I" and process.args : "*sh")) ) ) ) or /* shells specified in parent args */ /* nice rule is broken in 8.2 */ (process.parent.args : "*sh" and ( (process.parent.name == "nice") or (process.parent.name == "cpulimit" and process.parent.args == "-f") or (process.parent.name == "find" and process.parent.args == "." and process.parent.args == "-exec" and process.parent.args == ";" and process.parent.args : "/bin/*sh") or (process.parent.name == "flock" and process.parent.args == "-u" and process.parent.args == "/") ) ) )) or /* shells specified in args */ (process.args : "*sh" 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 event.action == "exec" and process.args_count == 2 and process.args : "*sh" and not process.executable : "/var/lib/docker/overlay2/*/merged/bin/busybox" and not (process.parent.args == "init" and process.parent.args == "runc") and not process.parent.args in ("ls-remote", "push", "fetch") and not process.parent.name == "mkinitramfs") or (process.name == "env" and process.args_count == 2 and process.args : "*sh") or (process.parent.name in ("vi", "vim") and process.parent.args == "-c" and process.parent.args : ":!*sh") or (process.parent.name in ("c89", "c99", "gcc") and process.parent.args : "*sh,-s" and process.parent.args == "-wrapper") or (process.parent.name == "expect" and process.parent.args == "-c" and process.parent.args : "spawn *sh;interact") or (process.parent.name == "mysql" and process.parent.args == "-e" and process.parent.args : "\\!*sh") or (process.parent.name == "ssh" and process.parent.args == "-o" and process.parent.args : "ProxyCommand=;*sh 0<&2 1>&2") ) ''' [[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/"