Analysis by: Wilbert Luy

 PLATFORM:

Linux

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size: 1,094,648 bytes
File Type: ELF
Memory Resident: No
Initial Samples Received Date: 30 Aug 2019
Payload: Connects to URLs/IPs, Downloads files, Deletes files

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Trojan drops the following files:

  • /lib64/security/pam_unix.so -> if 64-bit, compromised pam_unix.so file
  • /lib/x86_64-linux-gnu/security/pam_unix.so -> if 32-bit, compromised pam_unix.so file
  • /root/.ssh/authorized_keys

Other System Modifications

This Trojan deletes the following files:

  • /usr/bin/kaudited
  • /usr/bin/kswaped
  • /usr/bin/irqbalanced
  • /usr/bin/rctlcli
  • /usr/bin/systemd-network
  • /usr/bin/pamdicks
  • /lib/udev/ssd_control/iproute.ko
  • /lib/udev/ssd_control/netlink.ko
  • /lib/udev/ssd_control/cryptov2.ko

Process Termination

This Trojan terminates the following processes if found running in the affected system's memory:

  • kaudeited
  • kswaped
  • systemd-network
  • rctlcli
  • irqbalanced
  • ip6network
  • pamdicks

Download Routine

This Trojan connects to the following website(s) to download and execute a malicious file:

  • http://pm.{BLOCKED}llet.tk/cos7.tar.gz

It saves the files it downloads using the following names:

  • /usr/include/cos7.tar.gz

Other Details

This Trojan does the following:

  • Checks if OS is centos or redhat, if not it will connect and download from the following URL(s):
    http://pm.{BLOCKED}llet.tk/miner2
    It will save and execute the downloaded file as:
    tmp/miner2
  • It creates a copy of "/usr/bin/pamdicks.org" and saves it as "tmp/mmm" and "/usr/bin/mmm"
  • It changes the file attribute of "/etc/cron.d" to remove immutable and append only
  • Adds the following lines to "/etc/cron.d/watch":
    0 1 * * * root /bin/cp /usr/bin/mmm /tmp/mmm && /tmp/mmm
  • It changes the file attribute of every file in "/etc/cron.d" to include immutable
  • It checks for "usr/bin/chattr" or "/bin/chattr", if not accessible it will execute the following commands:
    /bin/mv /usr/bin/chattr /usr/bin/t
    /usr/bin/t +i /root/.ssh/authorized_keys
  • It checks for the presence of the following files:
    /lib64/security/pam_unix.so
    /lib/x86_64-linux-gnu/security/pam_unix.so.
    If present, it will replace it with a malicious copy of "pam_unix.so", otherwise it will create its own "pam_unix.so"
  • It checks if setenforce is running, if found running it will execute the following command:
    execute (setenforce 0)
  • It checks for /root/.ssh, if present it will change the file attribute to remove immutable and append only in all the files under that directory.
    If not present, it will create its own "/root/.ssh"
  • It sets the following configurations:
    SELINUX=disabled
    SELINUXTYPE=targeted, to disabled setenforce

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.340.04
FIRST VSAPI PATTERN DATE: 02 Sep 2019
VSAPI OPR PATTERN File: 15.341.00
VSAPI OPR PATTERN Date: 03 Sep 2019

Scan your computer with your Trend Micro product to delete files detected as Trojan.Linux.SKIDMAP.UWEJX. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check the following Trend Micro Support pages for more information:


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