Web Shell Detection: Script Process Child of Common Web Processes

  1[metadata]
  2creation_date = "2021/08/24"
  3integration = ["endpoint", "windows", "system"]
  4maturity = "production"
  5min_stack_comments = "New fields added: required_fields, related_integrations, setup"
  6min_stack_version = "8.3.0"
  7updated_date = "2024/03/28"
  8
  9[rule]
 10author = ["Elastic"]
 11description = "Identifies suspicious commands executed via a web server, which may suggest a vulnerability and remote shell access."
 12false_positives = [
 13    """
 14    Security audits, maintenance, and network administrative scripts may trigger this alert when run under web
 15    processes.
 16    """,
 17]
 18from = "now-9m"
 19index = ["winlogbeat-*", "logs-endpoint.events.process-*", "logs-windows.*", "endgame-*", "logs-system.security*"]
 20language = "eql"
 21license = "Elastic License v2"
 22name = "Web Shell Detection: Script Process Child of Common Web Processes"
 23note = """## Triage and analysis
 24
 25### Investigating Web Shell Detection: Script Process Child of Common Web Processes
 26
 27Adversaries may backdoor web servers with web shells to establish persistent access to systems. A web shell is a web script that is placed on an openly accessible web server to allow an adversary to use the web server as a gateway into a network. A web shell may provide a set of functions to execute or a command-line interface on the system that hosts the web server.
 28
 29This rule detects a web server process spawning script and command-line interface programs, potentially indicating attackers executing commands using the web shell.
 30
 31#### Possible investigation steps
 32
 33- Investigate abnormal behaviors observed by the subject process such as network connections, registry or file modifications, and any other spawned child processes.
 34- Examine the command line to determine which commands or scripts were executed.
 35- Investigate other alerts associated with the user/host during the past 48 hours.
 36- Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
 37- If scripts or executables were dropped, retrieve the files and determine if they are malicious:
 38  - Use a private sandboxed malware analysis system to perform analysis.
 39    - Observe and collect information about the following activities:
 40      - Attempts to contact external domains and addresses.
 41      - File and registry access, modification, and creation activities.
 42      - Service creation and launch activities.
 43      - Scheduled task creation.
 44  - Use the PowerShell Get-FileHash cmdlet to get the files' SHA-256 hash values.
 45    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 46
 47### False positive analysis
 48
 49- This activity is unlikely to happen legitimately. Any activity that triggered the alert and is not inherently malicious must be monitored by the security team.
 50
 51### Response and remediation
 52
 53- Initiate the incident response process based on the outcome of the triage.
 54- Isolate the involved host to prevent further post-compromise behavior.
 55- If the triage identified malware, search the environment for additional compromised hosts.
 56  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 57  - Stop suspicious processes.
 58  - Immediately block the identified indicators of compromise (IoCs).
 59  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 60- Remove and block malicious artifacts identified during triage.
 61- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business systems, and web services.
 62- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 63- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 64- 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).
 65"""
 66references = [
 67    "https://www.microsoft.com/security/blog/2020/02/04/ghost-in-the-shell-investigating-web-shell-attacks/",
 68    "https://www.elastic.co/security-labs/elastic-response-to-the-the-spring4shell-vulnerability-cve-2022-22965",
 69    "https://www.elastic.co/security-labs/hunting-for-persistence-using-elastic-security-part-1",
 70]
 71risk_score = 73
 72rule_id = "2917d495-59bd-4250-b395-c29409b76086"
 73setup = """## Setup
 74
 75If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
 76events will not define `event.ingested` and default fallback for EQL rules was not added until version 8.2.
 77Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
 78`event.ingested` to @timestamp.
 79For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
 80"""
 81severity = "high"
 82tags = ["Domain: Endpoint", "OS: Windows", "Use Case: Threat Detection", "Tactic: Persistence", "Tactic: Initial Access", "Tactic: Execution", "Resources: Investigation Guide", "Data Source: Elastic Endgame", "Data Source: Elastic Defend"]
 83timestamp_override = "event.ingested"
 84type = "eql"
 85
 86query = '''
 87process where host.os.type == "windows" and event.type == "start" and
 88  process.parent.name : ("w3wp.exe", "httpd.exe", "nginx.exe", "php.exe", "php-cgi.exe", "tomcat.exe") and
 89  process.name : ("cmd.exe", "cscript.exe", "powershell.exe", "pwsh.exe", "powershell_ise.exe", "wmic.exe", "wscript.exe") and
 90  not 
 91  (
 92    process.parent.name : ("php.exe", "httpd.exe") and process.name : "cmd.exe" and
 93    process.command_line : (
 94      "cmd.exe /c mode CON",
 95      "cmd.exe /s /c \"mode CON\"",
 96      "cmd.exe /c \"mode\"",
 97      "cmd.exe /s /c \"tput colors 2>&1\""
 98    )
 99  )
100'''
101
102
103[[rule.threat]]
104framework = "MITRE ATT&CK"
105[[rule.threat.technique]]
106id = "T1505"
107name = "Server Software Component"
108reference = "https://attack.mitre.org/techniques/T1505/"
109[[rule.threat.technique.subtechnique]]
110id = "T1505.003"
111name = "Web Shell"
112reference = "https://attack.mitre.org/techniques/T1505/003/"
113
114
115
116[rule.threat.tactic]
117id = "TA0003"
118name = "Persistence"
119reference = "https://attack.mitre.org/tactics/TA0003/"
120[[rule.threat]]
121framework = "MITRE ATT&CK"
122[[rule.threat.technique]]
123id = "T1190"
124name = "Exploit Public-Facing Application"
125reference = "https://attack.mitre.org/techniques/T1190/"
126
127
128[rule.threat.tactic]
129id = "TA0001"
130name = "Initial Access"
131reference = "https://attack.mitre.org/tactics/TA0001/"
132
133[[rule.threat]]
134framework = "MITRE ATT&CK"
135[[rule.threat.technique]]
136id = "T1059"
137name = "Command and Scripting Interpreter"
138reference = "https://attack.mitre.org/techniques/T1059/"
139[[rule.threat.technique.subtechnique]]
140id = "T1059.001"
141name = "PowerShell"
142reference = "https://attack.mitre.org/techniques/T1059/001/"
143[[rule.threat.technique.subtechnique]]
144id = "T1059.003"
145name = "Windows Command Shell"
146reference = "https://attack.mitre.org/techniques/T1059/003/"
147[[rule.threat.technique.subtechnique]]
148id = "T1059.005"
149name = "Visual Basic"
150reference = "https://attack.mitre.org/techniques/T1059/005/"
151
152
153[[rule.threat.technique]]
154id = "T1047"
155name = "Windows Management Instrumentation"
156reference = "https://attack.mitre.org/techniques/T1047/"
157
158
159
160[rule.threat.tactic]
161id = "TA0002"
162name = "Execution"
163reference = "https://attack.mitre.org/tactics/TA0002/"