Detect Dylib Hijacking in Microsoft Sentinel
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/
KQL Detection Query
DeviceFileEvents
| where Timestamp > ago(24h)
| where FileName endswith ".dylib"
| where FolderPath has_any ("/tmp/", "/var/folders/", "/Users/", "/Library/Application Support/")
| where ActionType in ("FileCreated", "FileModified")
| join kind=leftouter (
DeviceProcessEvents
| where Timestamp > ago(24h)
| project DeviceId, ProcessId, FileName, FolderPath, AccountName
) on DeviceId, $left.InitiatingProcessId == $right.ProcessId
| project Timestamp, DeviceName, AccountName,
DylibName=FileName, DylibPath=FolderPath,
CreatingProcess=FileName1,
SHA256
| sort by Timestamp descDetects dylib files created or modified in user-accessible paths on macOS. Focuses on dylib drops in temporary directories, user Library paths, and Application Support — common targets for dylib hijacking. The query identifies the process responsible for creating the dylib, which helps distinguish malicious drops from legitimate library updates.
Data Sources
Required Tables
False Positives & Tuning
- Software installation processes legitimately creating dylibs in Application Support or Library directories
- Homebrew and macOS package managers creating dylibs in user-accessible paths
- Developer builds and Xcode project compilation dropping dylibs in temp directories
- macOS system updates temporarily staging dylibs in writable directories before installation
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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