Potential Remote Code Execution via Web Server

  1[metadata]
  2creation_date = "2023/03/04"
  3integration = ["endpoint"]
  4maturity = "production"
  5min_stack_comments = "New fields added: required_fields, related_integrations, setup"
  6min_stack_version = "8.3.0"
  7updated_date = "2023/08/24"
  8
  9[transform]
 10[[transform.osquery]]
 11label = "Osquery - Retrieve Listening Ports"
 12query = "SELECT pid, address, port, socket, protocol, path FROM listening_ports"
 13
 14[[transform.osquery]]
 15label = "Osquery - Retrieve Open Sockets"
 16query = "SELECT pid, family, remote_address, remote_port, socket, state FROM process_open_sockets"
 17
 18[[transform.osquery]]
 19label = "Osquery - Retrieve Process Info"
 20query = "SELECT name, cmdline, parent, path, uid FROM processes"
 21
 22[[transform.osquery]]
 23label = "Osquery - Retrieve Process Info for Webapp User"
 24query = "SELECT name, cmdline, parent, path, uid FROM processes WHERE uid = {{process.user.id}}"
 25
 26[[transform.osquery]]
 27label = "Osquery - Retrieve Crontab Information"
 28query = "SELECT * FROM crontab"
 29
 30[rule]
 31author = ["Elastic"]
 32description = """
 33Identifies suspicious commands executed via a web server, which may suggest a vulnerability and remote shell access. 
 34Attackers may exploit a vulnerability in a web application to execute commands via a web server, or place a backdoor 
 35file that can be abused to gain code execution as a mechanism for persistence.
 36"""
 37false_positives = [
 38    """
 39    Network monitoring or management products may have a web server component that runs shell commands as part of normal
 40    behavior.
 41    """,
 42]
 43from = "now-9m"
 44index = ["logs-endpoint.events.*", "endgame-*"]
 45language = "eql"
 46license = "Elastic License v2"
 47name = "Potential Remote Code Execution via Web Server"
 48note = """## Triage and analysis
 49
 50### Investigating Potential Remote Code Execution via Web Server
 51
 52Adversaries may backdoor web servers with web shells to establish persistent access to systems. A web shell is a malicious script, often embedded into a compromised web server, that grants an attacker remote access and control over the server. This enables the execution of arbitrary commands, data exfiltration, and further exploitation of the target network.
 53
 54This rule detects a web server process spawning script and command line interface programs, potentially indicating attackers executing commands using the web shell.
 55
 56> **Note**:
 57> This investigation guide uses the [Osquery Markdown Plugin](https://www.elastic.co/guide/en/security/master/invest-guide-run-osquery.html) introduced in Elastic Stack version 8.5.0. Older Elastic Stack versions will display unrendered Markdown in this guide.
 58> This investigation guide uses [placeholder fields](https://www.elastic.co/guide/en/security/current/osquery-placeholder-fields.html) to dynamically pass alert data into Osquery queries. Placeholder fields were introduced in Elastic Stack version 8.7.0. If you're using Elastic Stack version 8.6.0 or earlier, you'll need to manually adjust this investigation guide's queries to ensure they properly run.
 59
 60#### Possible investigation steps
 61
 62- Investigate abnormal behaviors by the subject process such as network connections, file modifications, and any other spawned child processes.
 63  - Investigate listening ports and open sockets to look for potential reverse shells or data exfiltration.
 64    - $osquery_0
 65    - $osquery_1
 66  - Investigate the process information for malicious or uncommon processes/process trees.
 67    - $osquery_2
 68  - Investigate the process tree spawned from the user that is used to run the web application service. A user that is running a web application should not spawn other child processes.
 69    - $osquery_3
 70- Examine the command line to determine which commands or scripts were executed.
 71- Investigate other alerts associated with the user/host during the past 48 hours.
 72- If scripts or executables were dropped, retrieve the files and determine if they are malicious:
 73  - Use a private sandboxed malware analysis system to perform analysis.
 74    - Observe and collect information about the following activities:
 75      - Attempts to contact external domains and addresses.
 76        - Check if the domain is newly registered or unexpected.
 77        - Check the reputation of the domain or IP address.
 78      - File access, modification, and creation activities.
 79      - Cron jobs, services and other persistence mechanisms.
 80        - $osquery_4
 81
 82### False positive analysis
 83
 84- 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.
 85
 86### Response and remediation
 87
 88- Initiate the incident response process based on the outcome of the triage.
 89- Isolate the involved host to prevent further post-compromise behavior.
 90- If the triage identified malware, search the environment for additional compromised hosts.
 91  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 92  - Stop suspicious processes.
 93  - Immediately block the identified indicators of compromise (IoCs).
 94  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 95- Remove and block malicious artifacts identified during triage.
 96- 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.
 97- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 98- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 99- Leverage the incident response data and logging to improve the mean time to detect (MTTD) and the mean time to respond (MTTR).
100"""
101references = [
102    "https://pentestlab.blog/tag/web-shell/",
103    "https://www.elastic.co/security-labs/elastic-response-to-the-the-spring4shell-vulnerability-cve-2022-22965",
104]
105risk_score = 73
106rule_id = "f16fca20-4d6c-43f9-aec1-20b6de3b0aeb"
107severity = "high"
108tags = ["Domain: Endpoint", "OS: Linux", "Use Case: Threat Detection", "Tactic: Persistence", "Tactic: Initial Access", "Data Source: Elastic Endgame", "Use Case: Vulnerability", "Resources: Investigation Guide", "Data Source: Elastic Defend"]
109timestamp_override = "event.ingested"
110type = "eql"
111query = '''
112process where host.os.type == "linux" and event.type == "start" and
113event.action in ("exec", "exec_event") and process.parent.executable : (
114  "/usr/sbin/nginx", "/usr/local/sbin/nginx",
115  "/usr/sbin/apache", "/usr/local/sbin/apache",
116  "/usr/sbin/apache2", "/usr/local/sbin/apache2",
117  "/usr/sbin/php*", "/usr/local/sbin/php*",
118  "/usr/sbin/lighttpd", "/usr/local/sbin/lighttpd",
119  "/usr/sbin/hiawatha", "/usr/local/sbin/hiawatha",
120  "/usr/local/bin/caddy", 
121  "/usr/local/lsws/bin/lswsctrl",
122  "*/bin/catalina.sh"
123) and
124process.name : ("*sh", "python*", "perl", "php*", "tmux") and
125process.args : ("whoami", "id", "uname", "cat", "hostname", "ip", "curl", "wget", "pwd") and
126not process.name == "phpquery"
127'''
128
129[[rule.threat]]
130framework = "MITRE ATT&CK"
131
132[[rule.threat.technique]]
133id = "T1505"
134name = "Server Software Component"
135reference = "https://attack.mitre.org/techniques/T1505/"
136
137[[rule.threat.technique.subtechnique]]
138id = "T1505.003"
139name = "Web Shell"
140reference = "https://attack.mitre.org/techniques/T1505/003/"
141
142[rule.threat.tactic]
143id = "TA0003"
144name = "Persistence"
145reference = "https://attack.mitre.org/tactics/TA0003/"
146
147[[rule.threat]]
148framework = "MITRE ATT&CK"
149
150[[rule.threat.technique]]
151id = "T1190"
152name = "Exploit Public-Facing Application"
153reference = "https://attack.mitre.org/techniques/T1190/"
154
155[rule.threat.tactic]
156id = "TA0001"
157name = "Initial Access"
158reference = "https://attack.mitre.org/tactics/TA0001/"