Detect Dylib Hijacking in Elastic Security
Adversaries on macOS may execute malicious payloads by placing a malicious dynamic library (dylib) in a path that a victim application searches at runtime. The macOS dynamic linker searches paths in order: @rpath (relative run-path), @loader_path, @executable_path, and standard system paths (/usr/lib, /System/Library). If an application references a dylib with a weak link (LC_LOAD_WEAK_DYLIB) and the dylib does not exist, an adversary can plant a malicious dylib with the correct name at the expected path. The Empire post-exploitation framework includes modules specifically for scanning and exploiting dylib hijacking vulnerabilities.
MITRE ATT&CK
- Technique
- T1574 Hijack Execution Flow
- Sub-technique
- T1574.004 Dylib Hijacking
- Canonical reference
- https://attack.mitre.org/techniques/T1574/004/
Elastic Detection Query
file where host.os.type == "macos" and event.action in ("creation", "modification") and file.extension == "dylib" and (
file.path like "/tmp/*" or
file.path like "/var/folders/*" or
file.path like "/Users/*/Library/*" or
file.path like "/private/tmp/*" or
file.path like "/Users/*/Library/Application Support/*"
)Detects creation or modification of dynamic library (.dylib) files in suspicious macOS paths associated with dylib hijacking. Adversaries plant malicious dylibs in directories searched by the macOS dynamic linker (@rpath, @loader_path) to intercept application library loading.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate software installation or update processes writing dylibs to /Users/ paths (e.g., Homebrew, MacPorts installing user-local libraries)
- Developer workflows compiling and testing shared libraries in temporary build directories under /var/folders/
- System administration tools like Chef, Puppet, or Ansible deploying application libraries to non-standard paths
Other platforms for T1574.004
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1List Vulnerable Applications Using otool
Expected signal: Process creation event for otool. No file creation events generated. This is a read-only reconnaissance action. macOS audit logs (if enabled) would show the file read operations.
- Test 2Create Malicious Dylib in @rpath Location
Expected signal: File creation event for .dylib file in user Library path. Process creation events for gcc (if installed). The dylib file will appear as unsigned in code signing checks (codesign -v ~/Library/test-hijack/libtest.dylib).
- Test 3Verify DYLD Environment Variable Propagation
Expected signal: Process creation event for ls with DYLD_PRINT_LIBRARIES environment variable set. The output shows which dylibs ls loads. macOS SIP (System Integrity Protection) may suppress DYLD_* variables for protected binaries.
References (6)
- https://attack.mitre.org/techniques/T1574/004/
- https://objective-see.com/blog/blog_0x46.html
- https://www.virusbulletin.com/uploads/pdf/magazine/2015/vb201503-dylib-hijacking.pdf
- https://malwareunicorn.org/workshops/macos_dylib_injection.html#5
- https://github.com/EmpireProject/Empire/blob/master/lib/modules/python/situational_awareness/host/osx/HijackScanner.py
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1574.004/T1574.004.md
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