Detect Thread Local Storage in CrowdStrike LogScale
Adversaries may inject malicious code into processes via thread local storage (TLS) callbacks in order to evade process-based defenses as well as possibly elevate privileges. TLS callback injection involves manipulating pointers inside a portable executable (PE) to redirect a process to malicious code before reaching the code's legitimate entry point. TLS callbacks are normally used by the OS to setup and/or cleanup data used by threads. Manipulating TLS callbacks may be performed by allocating and writing to specific offsets within a process' memory space using other Process Injection techniques such as Process Hollowing.
MITRE ATT&CK
- Technique
- T1055 Process Injection
- Sub-technique
- T1055.005 Thread Local Storage
- Canonical reference
- https://attack.mitre.org/techniques/T1055/005/
LogScale Detection Query
#event_simpleName=ProcessRollup2
| FileName = /(?i)svchost\.exe|rundll32\.exe|regsvr32\.exe|dllhost\.exe|explorer\.exe/
| ParentBaseFileName != /(?i)services\.exe|svchost\.exe|winlogon\.exe/
| ProcessStartTime_decimal as procStart
| TargetProcessId_decimal as SuspectPID
| join(
[#event_simpleName=NetworkConnectIP4
| RemoteAddressIP4 != /^10\.|^172\.(1[6-9]|2[0-9]|3[01])\.|^192\.168\.|^127\.|^169\.254\./
| ContextProcessId_decimal as SuspectPID
| ContextTimeStamp_decimal as netTime],
field=[aid, SuspectPID],
include=[RemoteAddressIP4, RemotePort, netTime]
)
| timeDeltaMs := netTime - procStart
| timeDeltaMs >= 0
| timeDeltaMs <= 5000
| select([ComputerName, UserName, ParentBaseFileName, FileName, RemoteAddressIP4, RemotePort, timeDeltaMs])
| sort(timeDeltaMs, order=asc)CrowdStrike LogScale (Humio) query joining ProcessRollup2 and NetworkConnectIP4 Falcon telemetry events by agent ID and process ID. Surfaces cases where Windows system host binaries spawned by unexpected parent processes establish outbound TCP connections to public IPs within 5 seconds of creation — matching the behavior of TLS callback shellcode that executes before the PE loader hands control to the main entry point.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike Falcon sensor itself may generate this pattern when its process injection monitoring creates ProcessRollup2 events for child processes it instruments, followed immediately by sensor telemetry network upload events attributed to the same PID.
- SCCM or Intune deployment agents that use rundll32.exe or regsvr32.exe as execution hosts for package deployment scripts and immediately report installation status to management infrastructure via HTTPS.
- Windows credential roaming or profile sync services that spawn svchost.exe instances for roaming profile downloads and connect immediately to domain controllers or cloud identity providers in a non-standard parent chain during logon storms.
Other platforms for T1055.005
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 1PE with TLS Callback - Compile and Execute
Expected signal: Sysmon Event ID 1: PowerShell execution. In a real TLS callback binary: execution trace would show TLS callback function executing before the PE entry point. Debuggers (x64dbg, WinDbg) would show the TLS callback break before OEP.
- Test 2Ursnif-style TLS Callback Chain Analysis
Expected signal: Sysmon Event ID 1: PowerShell reading PE headers of notepad.exe. Sysmon Event ID 11: No file creation (read-only operation). This is a defensive analysis technique, not an attack.
- Test 3Process Hollowing with TLS Callback Redirection
Expected signal: Sysmon Event ID 1: notepad.exe spawned by PowerShell. When using full technique: Sysmon Event ID 10 (ProcessAccess) with PROCESS_VM_WRITE rights, followed by process resume and immediate malicious activity before expected notepad initialization.
References (4)
- https://attack.mitre.org/techniques/T1055/005/
- https://www.fireeye.com/blog/threat-research/2017/11/ursnif-variant-malicious-tls-callback-technique.html
- https://www.endgame.com/blog/technical-blog/ten-process-injection-techniques-technical-survey-common-and-trending-process
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1055.005/T1055.005.md
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