Lightning Framework: New Undetected “Swiss Army Knife” Linux Malware ⚡

Lightning Framework is a new undetected Swiss Army Knife-like Linux malware that has modular plugins and the ability to install rootkits.

Year after year Linux environments increasingly become the target of malware due to continued threat actor interest in the space. Malware targeting Linux environments surged in 2021, with a large amount of innovation resulting in new malicious code, especially in ransomwares, trojans, and botnets. With the rise in use of the cloud, it is no wonder that malware innovation is still accelerating at breakneck speed in this realm.

This is a technical analysis of a previously undocumented and undetected Linux threat called the Lightning Framework. It is rare to see such an intricate framework developed for targeting Linux systems. Lightning is a modular framework we discovered that has a plethora of capabilities, and the ability to install multiple types of rootkit, as well as the capability to run plugins. The framework has both passive and active capabilities for communication with the threat actor, including opening up SSH on an infected machine, and a polymorphic malleable command and control configuration. We are releasing this blog for informational purposes. We do not have all the files that are referenced in the framework, but hope that this release will help others if they possess other pieces of the jigsaw puzzle. We have not observed this malware being used in attacks in the wild.

Technical Analysis of Lightning Framework

The framework consists of a downloader and core module, with a number of plugins. Some of the plugins used by the malware are open-source tools. Below is a figure of the framework layout:

Lightning framework new linux threat

Overview of the Modules

Name Name on Disk Description
Lightning.Downloader kbioset The persistent module that downloads the core module and its plugins
Lightning.Core kkdmflush The main module of the Lightning Framework
Linux.Plugin.Lightning.SsHijacker soss There is a reference to this module but no sample found in the wild yet.
Linux.Plugin.Lightning.Sshd sshod OpenSSH with hardcoded private and host keys
Linux.Plugin.Lightning.Nethogs nethoogs There is a reference to this module but no sample found in the wild yet. Presumably the software Nethogs
Linux.Plugin.Lightning.iftop iftoop There is a reference to this module but no sample found in the wild yet. Presumably the software iftop
Linux.Plugin.Lightning.iptraf iptraof There is a reference to this module but no sample found in the wild yet. Presumably the software IPTraf
Linux.Plugin.RootkieHide There is a reference to this module but no sample found in the wild yet. LD_PRELOAD Rootkit
Linux.Plugin.Kernel elastisearch.ko There is a reference to this module but no sample found in the wild yet. LKM Rootkit


The main function of the downloader module is to fetch the other components and execute the core module.

Lightning framework downloader result in Intezer AnalyzeLightning Downloader result in Intezer Analyze

The downloader module starts by checking if it is located in the working directory /usr/lib64/seahorses/ under the name kbioset. The framework makes heavy use of typosquatting and masquerading in order to remain undetected. The reference to seahorses masquerades the password and key manager software seahorse. If not it will relocate itself to that working directory and execute that copy. The downloader will fingerprint the host name and network adapters to generate a GUID, which will be sent to the command and control (C2) server. 

Building the GUID

The downloader will then contact the C2 to fetch the following modules and plugins:

  • Linux.Plugin.Lightning.SsHijacker
  • Linux.Plugin.Lightning.Sshd
  • Linux.Plugin.Lightning.Nethogs
  • Linux.Plugin.Lightning.iftop
  • Linux.Plugin.Lightning.iptraf
  • Lightning.Core

Resources fetched from the C2

The method of contacting the C2 will be described below in the malleable C2 section (click here to jump to that section). The downloader will then execute the core module (kkdmflush). 

lightning framework excution of core moduleExecution of the core module


The core module is the main module in this framework, it is able to receive commands from the C2 and execute the plugin modules. The module has many capabilities and uses a number of techniques to hide artifacts to remain running under the radar. 

The core module modifies the name of the calling thread of the module to kdmflush, to make it appear that it is a kernel thread. 

Using prctl to modify calling thread name

Next the core module sets up persistence by creating a script that is executed upon system boot. This is achieved by first creating a file located at /etc/rc.d/init.d/elastisearch. The name appears to typosquat elasticsearch. The following contents are written to the file:

# chkconfig:2345 90 20
/usr/lib64/seahorses/kbioset &

This script will execute the downloader module upon boot. The service is then added using the chkconfig utility. 

Creation of the init.d script and service

The timestamp of the file is modified to hide artifacts, a technique known as “timestomping”. The file has its last modified time edited to match that of either whoami, find, or su. It will look for each file respectively until it finds one. This technique is used for most of the files that the framework creates.

File timestamp modification function

The malware will attempt to hide its Process ID (PID) and any related network ports. This is achieved by writing the frameworks running PIDs to two files: hpi and hpo. These files are parsed and then the existence of the file proc/y.y is checked. If the file exists, it means that a rootkit has been installed. The PIDs are written to proc/y.y for use by the rootkit, which may scrub any reference to files running in the framework from commands such as ps and netstat.

Writing PID to proc/y.y if it exists (Indication that rootkit exists)

The core module will generate a GUID in the same manner as the downloader and contact the C2. The response is parsed and the command is executed. The core module has the following commands:

Command Description
SystemInfo Fingerprints the machine
PureShellCommand Runs Shell command
RunShellPure Starts the Linux.Plugin.Lightning.Sshd (SSH Daemon) plugin
CloseShellPure Terminates the Linux.Plugin.Lightning.Sshd plugin
Disconnect Exits the Core module
GetRemotePathInfo Collects the summary of given path
KeepAlive No action, connection remains alive
UploadFileHeader Checks access of file
FileEdit Gets contents of file and time meta
TryPassSSH Adds a public key to the root/.ssh/authorized_keys file
DeleteVecFile Deletes the specified file or path
PreDownloadFile Calculates a checksum of the file
DownloadFile Sends a file to the C2
DeleteGuid Removes the framework
UpdateVersion Calls the Downloader module to update the framework
UpdateRemoteVersion Updates the framework including the downloader
Socks5 Sets up a Socks5 proxy
RestorePlug The same as UpdateVersion
GetDomainSetting Fetches the contents of the malleable C2 configuration file (cpc)
SetDomainSetting Updates the contents of the malleable C2 configuration file (cpc)
InstallKernelHide Fetches the OS release
RemoveKernelHide Removes kernel module
UpdateKernelVersion Removes the kernel module and runs uname -r
OverrideFile Overwrites specified file
UploadFileContent Writes data sent from server to file
LocalPluginRequest Either write the LD_PRELOAD rootkit or LKM rootkit

Network Communication

Network communication in the Core and Downloader modules are performed over TCP sockets. The data is structured in JSON. The C2 is stored in a polymorphic encoded configuration file that is unique for every single creation. This means that configuration files will not be able to be detected through techniques such as hashes. The key is built into the start of the encoded file.

Encoded malleable C2 configuration profile

The dynamic XOR decoding routine 

The decoded configuration is structured in JSON. The default configuration in the analyzed sample uses a local IP address 10.2.22[.]67 with the port 33229

Decoded default configuration

There is a passive mode of communication available if the actor executes the RunShellPure command. This starts an SSH service on the infected machine with the Linux.Plugin.Lightning.Sshd plugin. The plugin is an OpenSSH daemon that has hardcoded private and host keys, allowing the attacker to SSH into the machine with their own SSH key, creating a secondary backdoor. 

Hardcoded keys inside the modified OpenSSH daemon


The Lightning Framework is an interesting malware as it is not common to see such a large framework developed for targeting Linux. Although we do not have all the files, we can infer some of the missing functionality based on strings and code of the modules that we do possess. Soon we will release a another blog about detection opportunities for Lightning Framework using osquery.

We would like to extend a huge thanks to our friends and partners at IBM and SentinelOne for their help during investigating this threat.

IOCs for Lightning Framework


File SHA256
Lightning.Downloader 48f9471c20316b295704e6f8feb2196dd619799edec5835734fc24051f45c5b7
Lightning.Core fd285c2fb4d42dde23590118dba016bf5b846625da3abdbe48773530a07bcd1e
Linux.Plugin.Lightning.Sshd ad16989a3ebf0b416681f8db31af098e02eabd25452f8d781383547ead395237

Detection Rules

title: Lightning Framework File Path
status: experimental
description: Detects creation of files related to Lightning Framework.
author: Intezer
   product: linux
   category: file_create
         - '/usr/lib64/seahorses/'
         - 'kbioset'
         - 'cpc'
         - 'kkdmflush'
         - 'soss'
         - 'sshod'
         - 'nethoogs'
         - 'iftoop'
         - 'iptraof'
   condition: selection1 and selection2
   - Unknown.
title: Lightning Default C2 Communication
status: experimental
description: Detects communication to default local ip for Lightning Framework
author: Intezer
  category: firewall
    dst_port: 33229
  condition: select_outgoing
  - Unknown. 


Tactic Technique ID Description
Persistence Boot or Logon Initialization Scripts T1037 An init.d script is used for persistence of downloader module
Persistence SSH Authorized Keys T1098.004 SSH keys can be added to the authorized_keys file
Defense Evasion Obfuscated Files or Information T1027 The C2 profile is encoded on disk
Defense Evasion Deobfuscate/Decode Files or Information T1140 The C2 profile is decoded with a dynamic XOR algorithm
Defense Evasion Hide Artifacts T1564 Many artifacts are hidden including ports, PIDs, and file timestamps
Defense Evasion Masquerading T1036 Many files are masqueraded as other files or tasks
Defense Evasion Rootkit T1014 LKM and LD_PRELOAD rootkits are used
Defense Evasion Timestomp T1070.006 Files created by Lightning are modified to match that of other utilities
Defense Evasion File Deletion T1070.004 The framework has the ability to remove itself
Discovery File and Directory Discovery T1083 The framework can list files and directories on infected systems
Discovery Network Service Discovery T1046 Multiple plugins can be used to perform network service discovery
Discovery Network Sniffing T1040 Multiple plugins can be used to perform network sniffing
Discovery System Information Discovery T1082 Lightning can perform detailed system fingerprinting
Command and Control Data Encoding T1132 Data from the C2 is encoded
Command and Control Non-Application Layer Protocol T1095 Communication with the C2 is performed over TCP
Command and Control Proxy T1090 The framework has the ability to start a Socks5 proxy
Command and Control Exfiltration Over C2 Channel T1041 Data can be exfiltrated

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