Analysis by: Raymart Christian Yambot
ALIASES:

Trojan.Linux.XZBackdoor (IKARUS)

 PLATFORM:

Linux

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • 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.

It takes advantage of certain vulnerabilities.

  TECHNICAL DETAILS

File Size: 1,773,076 bytes
File Type: Other
Memory Resident: Yes
Initial Samples Received Date: 22 Jan 2025
Payload: Drops files, Modifies 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:

  • {Installation Directory}/.libs/liblzma_la-crc64-fast.o → Legitimate copy of {Installation Directory}/.libs/liblzma_la-crc64_fast.o
  • {Installation Directory}/.libs/liblzma_la-crc32-fast.o → Legitimate copy of {Installation Directory}/.libs/liblzma_la-crc32_fast.o
  • {Installation Directory}/liblzma_la-crc64-fast.o
  • {Installation Directory}/liblzma.so.5.6.0

Other System Modifications

This Trojan modifies the following file(s):

  • {Installation Directory}/.libs/liblzma_la-crc64_fast.c
  • {Installation Directory}/.libs/liblzma_la-crc32_fast.c
  • {Installation Directory}/src/liblzma/check/crc64_fast.c
  • {Installation Directory}/src/liblzma/check/crc32_fast.c

Other Details

This Trojan does the following:

  • It will proceed with its malicious routine if the following conditions are met:
    • Checks if GNU indirect function support is enabled.
    • Requires shared library support.
    • Checks if the system is an x86-64 Linux environment.
    • Checks for CRC IFUNC (Indirect Function) codes.
    • Checks if GCC (GNU Compiler Collection) and GNU ld (GNU Linker) are installed on the system.
    • Checks for the presence of good-large_compressed.lzma and bad-3-corrupt_lzma2.xz.
    • Checks if liblzma/Makefile contains all of the following lines within its content:
      • am__uninstall_files_from_dir =
      • __get_cpuid(
      • am__install_max =
      • am__vpath_adj_setup =
      • am__include = include
      • all: all-recursive
    • LTLIBRARIES = \$(lib_LTLIBRARIES)
    • AM_V_CCLD = \$(am__v_CCLD_\$(V))
    • am__install_max =
    • Checks if libtool is configured to build position-independent code (PIC).
    • Checks if the environment is Debian-based or RPM-based (x86_64).
    • It checks if the hijacked functions and hidden payloads are properly injected in the following files:
      • {Installation Directory}/src/liblzma/check/crc64_fast.c
      • {Installation Directory}/src/liblzma/check/crc32_fast.c
      • {Installation Directory}/src/liblzma/check/crc_x86_clmul.h
      • {Installation Directory}/src/liblzma/check/crc_x86_clmul.h
    • Checks if libtool is configured to build with IFUNC-compatible flags.
    • Checks if lazy symbol resolution (-z lazy) is NOT enabled.
    • Checks if the malicious object file liblzma_la-crc64-fast.o exists.
  • Upon successful completion of the build process, the backdoor functionality will be compiled and linked into the following file:
    • {Installation Directory}/liblzma.so.5.6.0
  • It waits for an OpenSSH connection and indirectly loads the liblzma.so.5.6.0 file, which contains the malicious code.
  • It renames the following files to their original names if the build fails:
    • {Installation Directory}/liblzma_la-crc32-fast.o → .libs/liblzma_la-crc32_fast.o
    • {Installation Directory}/liblzma_la-crc64-fast.o → .libs/liblzma_la-crc64_fast.o

It takes advantage of the following vulnerabilities:

It deletes the following files to remove its traces in the system:

  • {Installation Directory}/.libs/liblzma.a
  • {Installation Directory}/.libs/liblzma.la
  • {Installation Directory}/.libs/liblzma.lai
  • {Installation Directory}/.libs/liblzma.so
  • {Installation Directory}/.libs/liblzma_la-crc64-fast.o
  • {Installation Directory}/.libs/liblzma_la-crc32-fast.o
  • {Installation Directory}/liblzma_la-crc64-fast.o

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 19.850.04
FIRST VSAPI PATTERN DATE: 20 Jan 2025
VSAPI OPR PATTERN File: 19.851.00
VSAPI OPR PATTERN Date: 21 Jan 2025

Scan your computer with your Trend Micro product to delete files detected as Trojan.Linux.XZBACKDOOR.A. 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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