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

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

Written by Ryan Robinson

    Share article
    FacebookTwitterLinkedInRedditCopy Link

    Top Blogs

    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

    NameName on DiskDescription
    Lightning.DownloaderkbiosetThe persistent module that downloads the core module and its plugins
    Lightning.CorekkdmflushThe main module of the Lightning Framework
    Linux.Plugin.Lightning.SsHijackersossThere is a reference to this module but no sample found in the wild yet.
    Linux.Plugin.Lightning.SshdsshodOpenSSH with hardcoded private and host keys
    Linux.Plugin.Lightning.NethogsnethoogsThere is a reference to this module but no sample found in the wild yet. Presumably the software Nethogs
    Linux.Plugin.Lightning.iftopiftoopThere is a reference to this module but no sample found in the wild yet. Presumably the software iftop
    Linux.Plugin.Lightning.iptrafiptraofThere is a reference to this module but no sample found in the wild yet. Presumably the software IPTraf
    Linux.Plugin.RootkieHidelibsystemd.so.2There is a reference to this module but no sample found in the wild yet. LD_PRELOAD Rootkit
    Linux.Plugin.Kernelelastisearch.koThere is a reference to this module but no sample found in the wild yet. LKM Rootkit

    Lightning.Downloader

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

    Lightning framework downloader result in Intezer Analyze
    Lightning 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 module
    Execution of the core module

    Lightning.Core

    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:

    #!/bin/bash
    # 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:

    CommandDescription
    SystemInfoFingerprints the machine
    PureShellCommandRuns Shell command
    RunShellPureStarts the Linux.Plugin.Lightning.Sshd (SSH Daemon) plugin
    CloseShellPureTerminates the Linux.Plugin.Lightning.Sshd plugin
    DisconnectExits the Core module
    GetRemotePathInfoCollects the summary of given path
    KeepAliveNo action, connection remains alive
    UploadFileHeaderChecks access of file
    FileEditGets contents of file and time meta
    TryPassSSHAdds a public key to the root/.ssh/authorized_keys file
    DeleteVecFileDeletes the specified file or path
    PreDownloadFileCalculates a checksum of the file
    DownloadFileSends a file to the C2
    DeleteGuidRemoves the framework
    UpdateVersionCalls the Downloader module to update the framework
    UpdateRemoteVersionUpdates the framework including the downloader
    Socks5Sets up a Socks5 proxy
    RestorePlugThe same as UpdateVersion
    GetDomainSettingFetches the contents of the malleable C2 configuration file (cpc)
    SetDomainSettingUpdates the contents of the malleable C2 configuration file (cpc)
    InstallKernelHideFetches the OS release
    RemoveKernelHideRemoves kernel module
    UpdateKernelVersionRemoves the kernel module and runs uname -r
    OverrideFileOverwrites specified file
    UploadFileContentWrites data sent from server to file
    LocalPluginRequestEither 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

    Summary

    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

    Hashes

    FileSHA256
    Lightning.Downloader48f9471c20316b295704e6f8feb2196dd619799edec5835734fc24051f45c5b7
    Lightning.Corefd285c2fb4d42dde23590118dba016bf5b846625da3abdbe48773530a07bcd1e
    Linux.Plugin.Lightning.Sshdad16989a3ebf0b416681f8db31af098e02eabd25452f8d781383547ead395237

    Sigma Detection Rules

    title: Lightning Framework File Path
    status: experimental
    description: Detects creation of files related to Lightning Framework.
    author: Intezer
    references:
       - https://www.intezer.com
    logsource:
       product: linux
       category: file_create
    detection:
       selection1:
          TargetFilename|startswith:
             - '/usr/lib64/seahorses/'
       selection2:   
          TargetFilename|contains:
             - 'kbioset'
             - 'cpc'
             - 'kkdmflush'
             - 'soss'
             - 'sshod'
             - 'nethoogs'
             - 'iftoop'
             - 'iptraof'
       condition: selection1 and selection2
    falsepositives:
       - Unknown.
    title: Lightning Default C2 Communication
    status: experimental
    description: Detects communication to default local ip for Lightning Framework
    author: Intezer
    references:
      - https://intezer.com
    logsource:
      category: firewall
    detection:
      select_outgoing:
        dst_ip: 10.2.22.67
        dst_port: 33229
      condition: select_outgoing
    falsepositives:
      - Unknown. 

    MITRE ATT&CK

    TacticTechniqueIDDescription
    PersistenceBoot or Logon Initialization ScriptsT1037An init.d script is used for persistence of downloader module
    PersistenceSSH Authorized KeysT1098.004SSH keys can be added to the authorized_keys file
    Defense EvasionObfuscated Files or InformationT1027The C2 profile is encoded on disk
    Defense EvasionDeobfuscate/Decode Files or InformationT1140The C2 profile is decoded with a dynamic XOR algorithm
    Defense EvasionHide ArtifactsT1564Many artifacts are hidden including ports, PIDs, and file timestamps
    Defense EvasionMasqueradingT1036Many files are masqueraded as other files or tasks
    Defense EvasionRootkitT1014LKM and LD_PRELOAD rootkits are used
    Defense EvasionTimestompT1070.006Files created by Lightning are modified to match that of other utilities
    Defense EvasionFile DeletionT1070.004The framework has the ability to remove itself
    DiscoveryFile and Directory DiscoveryT1083The framework can list files and directories on infected systems
    DiscoveryNetwork Service DiscoveryT1046Multiple plugins can be used to perform network service discovery
    DiscoveryNetwork SniffingT1040Multiple plugins can be used to perform network sniffing
    DiscoverySystem Information DiscoveryT1082Lightning can perform detailed system fingerprinting
    Command and ControlData EncodingT1132Data from the C2 is encoded
    Command and ControlNon-Application Layer ProtocolT1095Communication with the C2 is performed over TCP
    Command and ControlProxyT1090The framework has the ability to start a Socks5 proxy
    Command and ControlExfiltration Over C2 ChannelT1041Data can be exfiltrated
    Ryan Robinson

    Ryan is a security researcher analyzing malware and scripts. Formerly, he was a researcher on Anomali's Threat Research Team.

    © Intezer.com 2022 All rights reserved
    Launching Autonomous SecOps: Your Virtual, Algorithm-Driven Tier 1 SOC TeamLaunching Autonomous SecOps: Your Virtual, Algorithm-Driven Tier 1 SOC Team Learn more