Potential Successful Linux FTP Brute Force Attack Detected

An FTP (file transfer protocol) brute force attack is a method where an attacker systematically tries different combinations of usernames and passwords to gain unauthorized access to an FTP server, and if successful, the impact can include unauthorized data access, manipulation, or theft, compromising the security and integrity of the server and potentially exposing sensitive information. This rule identifies multiple consecutive authentication failures targeting a specific user account from the same source address and within a short time interval, followed by a successful authentication.

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Potential Successful Linux RDP Brute Force Attack Detected

An RDP (Remote Desktop Protocol) brute force attack involves an attacker repeatedly attempting various username and password combinations to gain unauthorized access to a remote computer via RDP, and if successful, the potential impact can include unauthorized control over the compromised system, data theft, or the ability to launch further attacks within the network, jeopardizing the security and confidentiality of the targeted system and potentially compromising the entire network infrastructure. This rule identifies multiple consecutive authentication failures targeting a specific user account within a short time interval, followed by a successful authentication.

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Potential Process Injection via LD_PRELOAD Environment Variable

This rule detects the execution of a process where the LD_PRELOAD environment variable is set. LD_PRELOAD can be used to inject a shared library into a binary at or prior to execution. A threat actor may do this in order to load a malicious shared library for the purposes of persistence, privilege escalation, and defense evasion. This activity is not common and will potentially indicate malicious or suspicious behavior.

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Suspicious Modprobe File Event

Detects file events involving kernel modules in modprobe configuration files, which may indicate unauthorized access or manipulation of critical kernel modules. Attackers may tamper with the modprobe files to load malicious or unauthorized kernel modules, potentially bypassing security measures, escalating privileges, or hiding their activities within the system.

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Suspicious Sysctl File Event

Monitors file events on sysctl configuration files (e.g., /etc/sysctl.conf, /etc/sysctl.d/*.conf) to identify potential unauthorized access or manipulation of system-level configuration settings. Attackers may tamper with the sysctl configuration files to modify kernel parameters, potentially compromising system stability, performance, or security.

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Suspicious Proc Pseudo File System Enumeration

This rule monitors for a rapid enumeration of 25 different proc cmd, stat, and exe files, which suggests an abnormal activity pattern. Such behavior could be an indicator of a malicious process scanning or gathering information about running processes, potentially for reconnaissance, privilege escalation, or identifying vulnerable targets.

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Potential Code Execution via Postgresql

This rule monitors for suspicious activities that may indicate an attacker attempting to execute arbitrary code within a PostgreSQL environment. Attackers can execute code via PostgreSQL as a result of gaining unauthorized access to a public facing PostgreSQL database or exploiting vulnerabilities, such as remote command execution and SQL injection attacks, which can result in unauthorized access and malicious actions, and facilitate post-exploitation activities for unauthorized access and malicious actions.

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Potential Reverse Shell via Suspicious Parent Process

This detection rule detects the creation of a shell through a suspicious parent child relationship. Any reverse shells spawned by the specified utilities that use a forked process to initialize the connection attempt will be captured through this rule. Attackers may spawn reverse shells to establish persistence onto a target system.

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Potential Reverse Shell via Java

This detection rule identifies the execution of a Linux shell process from a Java JAR application post an incoming network connection. This behavior may indicate reverse shell activity via a Java application.

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Potential Reverse Shell via Suspicious Child Process

This detection rule detects the creation of a shell through a suspicious process chain. Any reverse shells spawned by the specified utilities that are initialized from a single process followed by a network connection attempt will be captured through this rule. Attackers may spawn reverse shells to establish persistence onto a target system.

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Potential Reverse Shell via Suspicious Binary

This detection rule detects the creation of a shell through a chain consisting of the execution of a suspicious binary (located in a commonly abused location or executed manually) followed by a network event and ending with a shell being spawned. Stageless reverse tcp shells display this behaviour. Attackers may spawn reverse shells to establish persistence onto a target system.

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Potential Reverse Shell

This detection rule identifies suspicious network traffic patterns associated with TCP reverse shell activity. This activity consists of a parent-child relationship where a network event is followed by the creation of a shell process. An attacker may establish a Linux TCP reverse shell to gain remote access to a target system.

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Suspicious Content Extracted or Decompressed via Funzip

Identifies when suspicious content is extracted from a file and subsequently decompressed using the funzip utility. Malware may execute the tail utility using the "-c" option to read a sequence of bytes from the end of a file. The output from tail can be piped to funzip in order to decompress malicious code before it is executed. This behavior is consistent with malware families such as Bundlore.

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Suspicious System Commands Executed by Previously Unknown Executable

This rule monitors for the execution of several commonly used system commands executed by a previously unknown executable located in commonly abused directories. An alert from this rule can indicate the presence of potentially malicious activity, such as the execution of unauthorized or suspicious processes attempting to run malicious code. Detecting and investigating such behavior can help identify and mitigate potential security threats, protecting the system and its data from potential compromise.

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Suspicious Data Encryption via OpenSSL Utility

Identifies when the openssl command-line utility is used to encrypt multiple files on a host within a short time window. Adversaries may encrypt data on a single or multiple systems in order to disrupt the availability of their target’s data and may attempt to hold the organization’s data to ransom for the purposes of extortion.

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Kernel Load or Unload via Kexec Detected

This detection rule identifies the usage of kexec, helping to uncover unauthorized kernel replacements and potential compromise of the system’s integrity. Kexec is a Linux feature that enables the loading and execution of a different kernel without going through the typical boot process. Malicious actors can abuse kexec to bypass security measures, escalate privileges, establish persistence or hide their activities by loading a malicious kernel, enabling them to tamper with the system’s trusted state, allowing e.g. a VM Escape.

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Potential Network Sweep Detected

This rule identifies a potential network sweep. A network sweep is a method used by attackers to scan a target network, identifying active hosts, open ports, and available services to gather information on vulnerabilities and weaknesses. This reconnaissance helps them plan subsequent attacks and exploit potential entry points for unauthorized access, data theft, or other malicious activities. This rule proposes threshold logic to check for connection attempts from one source host to 10 or more destination hosts on commonly used network services.

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Potential Network Scan Detected

This rule identifies a potential port scan. A port scan is a method utilized by attackers to systematically scan a target system or network for open ports, allowing them to identify available services and potential vulnerabilities. By mapping out the open ports, attackers can gather critical information to plan and execute targeted attacks, gaining unauthorized access, compromising security, and potentially leading to data breaches, unauthorized control, or further exploitation of the targeted system or network. This rule proposes threshold logic to check for connection attempts from one source host to 20 or more destination ports.

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Potential SYN-Based Network Scan Detected

This rule identifies a potential SYN-Based port scan. A SYN port scan is a technique employed by attackers to scan a target network for open ports by sending SYN packets to multiple ports and observing the response. Attackers use this method to identify potential entry points or services that may be vulnerable to exploitation, allowing them to launch targeted attacks or gain unauthorized access to the system or network, compromising its security and potentially leading to data breaches or further malicious activities. This rule proposes threshold logic to check for connection attempts from one source host to 10 or more destination ports using 2 or less packets per port.

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First Time Seen Removable Device

Identifies newly seen removable devices by device friendly name using registry modification events. While this activity is not inherently malicious, analysts can use those events to aid monitoring for data exfiltration over those devices.

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Elastic Agent Service Terminated

Identifies the Elastic endpoint agent has stopped and is no longer running on the host. Adversaries may attempt to disable security monitoring tools in an attempt to evade detection or prevention capabilities during an intrusion. This may also indicate an issue with the agent itself and should be addressed to ensure defensive measures are back in a stable state.

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Suspicious Network Connection Attempt by Root

Identifies an outbound network connection attempt followed by a session id change as the root user by the same process entity. This particular instantiation of a network connection is abnormal and should be investigated as it may indicate a potential reverse shell activity via a privileged process.

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Potential SSH Password Guessing

Identifies multiple SSH login failures followed by a successful one from the same source address. Adversaries can attempt to login into multiple users with a common or known password to gain access to accounts.

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Potential External Linux SSH Brute Force Detected

Identifies multiple external consecutive login failures targeting a user account from the same source address within a short time interval. Adversaries will often brute force login attempts across multiple users with a common or known password, in an attempt to gain access to these accounts.

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Potential Internal Linux SSH Brute Force Detected

Identifies multiple internal consecutive login failures targeting a user account from the same source address within a short time interval. Adversaries will often brute force login attempts across multiple users with a common or known password, in an attempt to gain access to these accounts.

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Attempt to Disable Syslog Service

Adversaries may attempt to disable the syslog service in an attempt to an attempt to disrupt event logging and evade detection by security controls.

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Abnormal Process ID or Lock File Created

Identifies the creation of a Process ID (PID), lock or reboot file created in temporary file storage paradigm (tmpfs) directory /var/run. On Linux, the PID files typically hold the process ID to track previous copies running and manage other tasks. Certain Linux malware use the /var/run directory for holding data, executables and other tasks, disguising itself or these files as legitimate PID files.

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Interactive Terminal Spawned via Python

Identifies when a terminal (tty) is spawned via Python. Attackers may upgrade a simple reverse shell to a fully interactive tty after obtaining initial access to a host.

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Linux Restricted Shell Breakout via Linux Binary(s)

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.

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Suspicious File Changes Activity Detected

This rule identifies a sequence of 100 file extension rename events within a set of common file paths by the same process in a timespan of 1 second. Ransomware is a type of malware that encrypts a victim’s files or systems and demands payment (usually in cryptocurrency) in exchange for the decryption key. One important indicator of a ransomware attack is the mass encryption of the file system, after which a new file extension is added to the file.

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Potential Linux Ransomware Note Creation Detected

This rule identifies a sequence of a mass file encryption event in conjunction with the creation of a .txt file with a file name containing ransomware keywords executed by the same process in a 1 second timespan. Ransomware is a type of malware that encrypts a victim’s files or systems and demands payment (usually in cryptocurrency) in exchange for the decryption key. One important indicator of a ransomware attack is the mass encryption of the file system, after which a new file extension is added to the file.

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High Number of Process Terminations

This rule identifies a high number (10) of process terminations via pkill from the same host within a short time period.

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Chkconfig Service Add

Detects the use of the chkconfig binary to manually add a service for management by chkconfig. Threat actors may utilize this technique to maintain persistence on a system. When a new service is added, chkconfig ensures that the service has either a start or a kill entry in every runlevel and when the system is rebooted the service file added will run providing long-term persistence.

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Suspicious File Creation in /etc for Persistence

Detects the manual creation of files in specific etc directories, via user root, used by Linux malware to persist and elevate privileges on compromised systems. File creation in these directories should not be entirely common and could indicate a malicious binary or script installing persistence mechanisms for long term access.

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Modification of Dynamic Linker Preload Shared Object

Identifies modification of the dynamic linker preload shared object (ld.so.preload). Adversaries may execute malicious payloads by hijacking the dynamic linker used to load libraries.

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Potential Shadow File Read via Command Line Utilities

Identifies access to the /etc/shadow file via the commandline using standard system utilities. After elevating privileges to root, threat actors may attempt to read or dump this file in order to gain valid credentials. They may utilize these to move laterally undetected and access additional resources.

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Multiple Vault Web Credentials Read

Windows Credential Manager allows you to create, view, or delete saved credentials for signing into websites, connected applications, and networks. An adversary may abuse this to list or dump credentials stored in the Credential Manager for saved usernames and passwords. This may also be performed in preparation of lateral movement.

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Suspicious Antimalware Scan Interface DLL

Identifies the creation of the Antimalware Scan Interface (AMSI) DLL in an unusual location. This may indicate an attempt to bypass AMSI by loading a rogue AMSI module instead of the legit one.

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Unusual File Creation - Alternate Data Stream

Identifies suspicious creation of Alternate Data Streams on highly targeted files. This is uncommon for legitimate files and sometimes done by adversaries to hide malware.

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Suspicious PowerShell Engine ImageLoad

Identifies the PowerShell engine being invoked by unexpected processes. Rather than executing PowerShell functionality with powershell.exe, some attackers do this to operate more stealthily.

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Incoming Execution via WinRM Remote Shell

Identifies remote execution via Windows Remote Management (WinRM) remote shell on a target host. This could be an indication of lateral movement.

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WMI Incoming Lateral Movement

Identifies processes executed via Windows Management Instrumentation (WMI) on a remote host. This could be indicative of adversary lateral movement, but could be noisy if administrators use WMI to remotely manage hosts.

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Incoming Execution via PowerShell Remoting

Identifies remote execution via Windows PowerShell remoting. Windows PowerShell remoting allows a user to run any Windows PowerShell command on one or more remote computers. This could be an indication of lateral movement.

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RDP Enabled via Registry

Identifies registry write modifications to enable Remote Desktop Protocol (RDP) access. This could be indicative of adversary lateral movement preparation.

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Remotely Started Services via RPC

Identifies remote execution of Windows services over remote procedure call (RPC). This could be indicative of lateral movement, but will be noisy if commonly done by administrators."

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A scheduled task was updated

Indicates the update of a scheduled task using Windows event logs. Adversaries can use these to establish persistence, by changing the configuration of a legit scheduled task. Some changes such as disabling or enabling a scheduled task are common and may may generate noise.

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Suspicious DLL Loaded for Persistence or Privilege Escalation

Identifies the loading of a non Microsoft signed DLL that is missing on a default Windows install (phantom DLL) or one that can be loaded from a different location by a native Windows process. This may be abused to persist or elevate privileges via privileged file write vulnerabilities.

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Potential SSH Brute Force Detected on Privileged Account

Identifies multiple consecutive login failures targeting a root user account from the same source address and within a short time interval. Adversaries will often brute force login attempts on privileged accounts with a common or known password, in an attempt to gain privileged access to systems.

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Reverse Shell Created via Named Pipe

Identifies a reverse shell via the abuse of named pipes on Linux with the help of OpenSSL or Netcat. First in, first out (FIFO) files are special files for reading and writing to by Linux processes. For this to work, a named pipe is created and passed to a Linux shell where the use of a network connection tool such as Netcat or OpenSSL has been established. The stdout and stderr are captured in the named pipe from the network connection and passed back to the shell for execution.

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