[metadata]
creation_date = "2023/07/04"
integration = ["auditd_manager"]
maturity = "production"
min_stack_comments = "The sampling feature within EQL was introduced in 8.6.0"
min_stack_version = "8.6.0"
updated_date = "2023/10/16"

[rule]
author = ["Elastic"]
description = """
This detection rule identifies suspicious network traffic patterns associated with UDP reverse shell activity. This 
activity consists of a sample of an execve, socket and connect syscall executed by the same process, where the
auditd.data.a0-1 indicate a UDP connection, ending with an egress connection event. An attacker may establish a Linux 
UDP reverse shell to bypass traditional firewall restrictions and gain remote access to a target system covertly.
"""
from = "now-9m"
index = ["auditbeat-*", "logs-auditd_manager.auditd-*"]
language = "eql"
license = "Elastic License v2"
name = "Potential Reverse Shell via UDP"
references = [
    "https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/Methodology%20and%20Resources/Reverse%20Shell%20Cheatsheet.md"
]
risk_score = 47
rule_id = "a5eb21b7-13cc-4b94-9fe2-29bb2914e037"
setup = """

This rule requires data coming in either from Auditbeat integration, or Auditd Manager integration.

### Auditbeat Setup
Auditbeat is a lightweight shipper that you can install on your servers to audit the activities of users and processes on your systems. For example, you can use Auditbeat to collect and centralize audit events from the Linux Audit Framework. You can also use Auditbeat to detect changes to critical files, like binaries and configuration files, and identify potential security policy violations.

#### The following steps should be executed in order to add the Auditbeat for Linux System:
- Elastic provides repositories available for APT and YUM-based distributions. Note that we provide binary packages, but no source packages.
- To install the APT and YUM repositories follow the setup instructions in this [helper guide](https://www.elastic.co/guide/en/beats/auditbeat/current/setup-repositories.html).
- To run Auditbeat on Docker follow the setup instructions in the [helper guide](https://www.elastic.co/guide/en/beats/auditbeat/current/running-on-docker.html).
- To run Auditbeat on Kubernetes follow the setup instructions in the [helper guide](https://www.elastic.co/guide/en/beats/auditbeat/current/running-on-kubernetes.html).
- For complete Setup and Run Auditbeat information refer to the [helper guide](https://www.elastic.co/guide/en/beats/auditbeat/current/setting-up-and-running.html).

### Auditd Manager Integration Setup
The Auditd Manager Integration receives audit events from the Linux Audit Framework which is a part of the Linux kernel.
Auditd Manager provides a user-friendly interface and automation capabilities for configuring and monitoring system auditing through the auditd daemon. With `auditd_manager`, administrators can easily define audit rules, track system events, and generate comprehensive audit reports, improving overall security and compliance in the system.

#### The following steps should be executed in order to add the Elastic Agent System integration "auditd_manager" on a Linux System:
- Go to the Kibana home page and click Add integrations.
- In the query bar, search for Auditd Manager and select the integration to see more details about it.
- Click Add Auditd Manager.
- Configure the integration name and optionally add a description.
- Review optional and advanced settings accordingly.
- Add the newly installed `auditd manager` to an existing or a new agent policy, and deploy the agent on a Linux system from which auditd log files are desirable.
- Click Save and Continue.
- For more details on the integeration refer to the [helper guide](https://docs.elastic.co/integrations/auditd_manager).

#### Rule Specific Setup Note
Auditd Manager subscribes to the kernel and receives events as they occur without any additional configuration.
However, if more advanced configuration is required to detect specific behavior, audit rules can be added to the integration in either the "audit rules" configuration box or the "auditd rule files" box by specifying a file to read the audit rules from.
- For this detection rule no additional audit rules are required to be added to the integration.

"""
severity = "medium"
tags = ["OS: Linux", "Use Case: Threat Detection", "Tactic: Execution"]
timestamp_override = "event.ingested"
type = "eql"
query = '''
sample by host.id, process.pid, process.parent.pid
[process where host.os.type == "linux" and event.dataset == "auditd_manager.auditd" and 
 auditd.data.syscall == "execve" and process.name : ("bash", "dash", "sh", "tcsh",
 "csh", "zsh", "ksh", "fish", "perl", "python*", "nc", "ncat", "netcat", "php*", "ruby",
 "openssl", "awk", "telnet", "lua*", "socat")]
[process where host.os.type == "linux" and event.dataset == "auditd_manager.auditd" and 
 auditd.data.syscall == "socket" and process.name : ("bash", "dash", "sh", "tcsh", "csh",
 "zsh", "ksh", "fish", "perl", "python*", "nc", "ncat", "netcat", "php*", "ruby", "openssl",
 "awk", "telnet", "lua*", "socat") and auditd.data.a0 == "2" and auditd.data.a1 : ("2", "802")]
[network where host.os.type == "linux" and event.dataset == "auditd_manager.auditd" and 
 auditd.data.syscall == "connect" and process.name : ("bash", "dash", "sh", "tcsh", "csh",
 "zsh", "ksh", "fish", "perl", "python*", "nc", "ncat", "netcat", "php*", "ruby", "openssl",
 "awk", "telnet", "lua*", "socat") and network.direction == "egress" and destination.ip != null and 
 destination.ip != "127.0.0.1" and destination.ip != "127.0.0.53" and destination.ip != "::1"]
'''

[[rule.threat]]
framework = "MITRE ATT&CK"

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

[[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]]
framework = "MITRE ATT&CK"

[rule.threat.tactic]
name = "Command and Control"
id = "TA0011"
reference = "https://attack.mitre.org/tactics/TA0011/"

[[rule.threat.technique]]
name = "Application Layer Protocol"
id = "T1071"
reference = "https://attack.mitre.org/techniques/T1071/"