Potential Masquerading as Business App Installer

Identifies executables with names resembling legitimate business applications but lacking signatures from the original developer. Attackers may trick users into downloading malicious executables that masquerade as legitimate applications via malicious ads, forum posts, and tutorials, effectively gaining initial access.

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Suspicious Execution from INET Cache

Identifies the execution of a process with arguments pointing to the INetCache Folder. Adversaries may deliver malicious content via WININET during initial access.

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Execution from a Removable Media with Network Connection

Identifies process execution from a removable media and by an unusual process. Adversaries may move onto systems, possibly those on disconnected or air-gapped networks, by copying malware to removable media and taking advantage of Autorun features when the media is inserted into a system and executes.

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Potential Remote File Execution via MSIEXEC

Identifies the execution of the built-in Windows Installer, msiexec.exe, to install a remote package. Adversaries may abuse msiexec.exe to launch local or network accessible MSI files.

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Remote XSL Script Execution via COM

Identifies the execution of a hosted XSL script using the Microsoft.XMLDOM COM interface via Microsoft Office processes. This behavior may indicate adversarial activity to execute malicious JScript or VBScript on the system.

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Network Activity Detected via cat

This rule monitors for the execution of the cat command, followed by a connection attempt by the same process. Cat is capable of transfering data via tcp/udp channels by redirecting its read output to a /dev/tcp or /dev/udp channel. This activity is highly suspicious, and should be investigated. Attackers may leverage this capability to transfer tools or files to another host in the network or exfiltrate data while attempting to evade detection in the process.

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Suspicious Utility Launched via ProxyChains

This rule monitors for the execution of suspicious linux tools through ProxyChains. ProxyChains is a command-line tool that enables the routing of network connections through intermediary proxies, enhancing anonymity and enabling access to restricted resources. Attackers can exploit the ProxyChains utility to hide their true source IP address, evade detection, and perform malicious activities through a chain of proxy servers, potentially masking their identity and intentions.

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Potential Linux Tunneling and/or Port Forwarding

This rule monitors for a set of Linux utilities that can be used for tunneling and port forwarding. Attackers can leverage tunneling and port forwarding techniques to bypass network defenses, establish hidden communication channels, and gain unauthorized access to internal resources, facilitating data exfiltration, lateral movement, and remote control.

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Potential Linux Credential Dumping via Unshadow

Identifies the execution of the unshadow utility which is part of John the Ripper, a password-cracking tool on the host machine. Malicious actors can use the utility to retrieve the combined contents of the /etc/shadow and /etc/password files. Using the combined file generated from the utility, the malicious threat actors can use them as input for password-cracking utilities or prepare themselves for future operations by gathering credential information of the victim.

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Linux init (PID 1) Secret Dump via GDB

This rule monitors for the potential memory dump of the init process (PID 1) through gdb. Attackers may leverage memory dumping techniques to attempt secret extraction from privileged processes. Tools that display this behavior include "truffleproc" and "bash-memory-dump". This behavior should not happen by default, and should be investigated thoroughly.

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Potential Linux Local Account Brute Force Detected

Identifies multiple consecutive login attempts executed by one process targeting a local linux user account within a short time interval. Adversaries might brute force login attempts across different users with a default wordlist or a set of customly crafted passwords in an attempt to gain access to these accounts.

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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 Linux Credential Dumping via Proc Filesystem

Identifies the execution of the mimipenguin exploit script which is linux adaptation of Windows tool mimikatz. Mimipenguin exploit script is used to dump clear text passwords from a currently logged-in user. The tool exploits a known vulnerability CVE-2018-20781. Malicious actors can exploit the cleartext credentials in memory by dumping the process and extracting lines that have a high probability of containing cleartext passwords.

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Attempt to Disable IPTables or Firewall

Adversaries may attempt to disable the iptables or firewall service in an attempt to affect how a host is allowed to receive or send network traffic.

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Base16 or Base32 Encoding/Decoding Activity

Adversaries may encode/decode data in an attempt to evade detection by host- or network-based security controls.

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108

System Binary Copied and/or Moved to Suspicious Directory

This rule monitors for the copying or moving of a system binary to a suspicious directory. Adversaries may copy/move and rename system binaries to evade detection. Copying a system binary to a different location should not occur often, so if it does, the activity should be investigated.

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Attempt to Clear Kernel Ring Buffer

Monitors for the deletion of the kernel ring buffer events through dmesg. Attackers may clear kernel ring buffer events to evade detection after installing a Linux kernel module (LKM).

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Potential Disabling of AppArmor

This rule monitors for potential attempts to disable AppArmor. AppArmor is a Linux security module that enforces fine-grained access control policies to restrict the actions and resources that specific applications and processes can access. Adversaries may disable security tools to avoid possible detection of their tools and activities.

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Potential Disabling of SELinux

Identifies potential attempts to disable Security-Enhanced Linux (SELinux), which is a Linux kernel security feature to support access control policies. Adversaries may disable security tools to avoid possible detection of their tools and activities.

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108

ESXI Timestomping using Touch Command

Identifies instances where the touch command is executed on a Linux system with the "-r" flag, which is used to modify the timestamp of a file based on another file’s timestamp. The rule targets specific VM-related paths, such as "/etc/vmware/", "/usr/lib/vmware/", or "/vmfs/*". These paths are associated with VMware virtualization software, and their presence in the touch command arguments may indicate that a threat actor is attempting to tamper with timestamps of VM-related files and configurations on the system.

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File Deletion via Shred

Malware or other files dropped or created on a system by an adversary may leave traces behind as to what was done within a network and how. Adversaries may remove these files over the course of an intrusion to keep their footprint low or remove them at the end as part of the post-intrusion cleanup process.

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108

File Permission Modification in Writable Directory

Identifies file permission modifications in common writable directories by a non-root user. Adversaries often drop files or payloads into a writable directory and change permissions prior to execution.

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209

Creation of Hidden Files and Directories via CommandLine

Users can mark specific files as hidden simply by putting a "." as the first character in the file or folder name. Adversaries can use this to their advantage to hide files and folders on the system for persistence and defense evasion. This rule looks for hidden files or folders in common writable directories.

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109

Creation of Hidden Shared Object File

Identifies the creation of a hidden shared object (.so) file. Users can mark specific files as hidden simply by putting a "." as the first character in the file or folder name. Adversaries can use this to their advantage to hide files and folders on the system for persistence and defense evasion.

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109

Kernel Module Removal

Kernel modules are pieces of code that can be loaded and unloaded into the kernel upon demand. They extend the functionality of the kernel without the need to reboot the system. This rule identifies attempts to remove a kernel module.

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108

Potential Hidden Process via Mount Hidepid

Identifies the execution of mount process with hidepid parameter, which can make processes invisible to other users from the system. Adversaries using Linux kernel version 3.2+ (or RHEL/CentOS v6.5+ above) can hide the process from other users. When hidepid=2 option is executed to mount the /proc filesystem, only the root user can see all processes and the logged-in user can only see their own process. This provides a defense evasion mechanism for the adversaries to hide their process executions from all other commands such as ps, top, pgrep and more. With the Linux kernel hardening hidepid option all the user has to do is remount the /proc filesystem with the option, which can now be monitored and detected.

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Potential Defense Evasion via PRoot

Identifies the execution of the PRoot utility, an open-source tool for user-space implementation of chroot, mount --bind, and binfmt_misc. Adversaries can leverage an open-source tool PRoot to expand the scope of their operations to multiple Linux distributions and simplify their necessary efforts. In a normal threat scenario, the scope of an attack is limited by the varying configurations of each Linux distribution. With PRoot, it provides an attacker with a consistent operational environment across different Linux distributions, such as Ubuntu, Fedora, and Alpine. PRoot also provides emulation capabilities that allow for malware built on other architectures, such as ARM, to be run.The post-exploitation technique called bring your own filesystem (BYOF), can be used by the threat actors to execute malicious payload or elevate privileges or perform network scans or orchestrate another attack on the environment. Although PRoot was originally not developed with malicious intent it can be easily tuned to work for one.

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Potential Pspy Process Monitoring Detected

This rule leverages auditd to monitor for processes scanning different processes within the /proc directory using the openat syscall. This is a strong indication for the usage of the pspy utility. Attackers may leverage the pspy process monitoring utility to monitor system processes without requiring root permissions, in order to find potential privilege escalation vectors.

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Potential Meterpreter Reverse Shell

This detection rule identifies a sample of suspicious Linux system file reads used for system fingerprinting, leveraged by the Metasploit Meterpreter shell to gather information about the target that it is executing its shell on. Detecting this pattern is indicative of a successful meterpreter shell connection.

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Potential Reverse Shell via UDP

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.

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Kernel Driver Load by non-root User

Detects the loading of a Linux kernel module by a non-root user through system calls. Threat actors may leverage Linux kernel modules to load a rootkit on a system providing them with complete control and the ability to hide from security products. As other rules monitor for the addition of Linux kernel modules through system utilities or .ko files, this rule covers the gap that evasive rootkits leverage by monitoring for kernel module additions on the lowest level through auditd_manager.

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Privilege Escalation via CAP_CHOWN/CAP_FOWNER Capabilities

Identifies instances where a processes (granted CAP_CHOWN and/or CAP_FOWNER capabilities) is executed, after which the ownership of a suspicious file or binary is changed. In Linux, the CAP_CHOWN capability allows a process to change the owner of a file, while CAP_FOWNER permits it to bypass permission checks on operations that require file ownership (like reading, writing, and executing). Attackers may abuse these capabilities to obtain unauthorized access to files.

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Suspicious Passwd File Event Action

Monitors for the generation of a passwd password entry via openssl, followed by a file write activity on the "/etc/passwd" file. The "/etc/passwd" file in Linux stores user account information, including usernames, user IDs, group IDs, home directories, and default shell paths. Attackers may exploit a misconfiguration in the "/etc/passwd" file permissions or other privileges to add a new entry to the "/etc/passwd" file with root permissions, and leverage this new user account to login as root.

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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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Process Created with a Duplicated Token

Identifies the creation of a process impersonating the token of another user logon session. Adversaries may create a new process with a different token to escalate privileges and bypass access controls.

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Interactive Logon by an Unusual Process

Identifies interactive logon attempt with alternate credentials and by an unusual process. Adversaries may create a new token to escalate privileges and bypass access controls.

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First Time Seen NewCredentials Logon Process

Identifies a new credentials logon type performed by an unusual process. This may indicate the existence of an access token forging capability that are often abused to bypass access control restrictions.

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