Process Injection: Thread Local Storage

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 is a method of executing arbitrary code in the address space of a separate live process.

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.[1]

Running code in the context of another process may allow access to the process's memory, system/network resources, and possibly elevated privileges. Execution via TLS callback injection may also evade detection from security products since the execution is masked under a legitimate process.

ID: T1055.005
Sub-technique of:  T1055
Platforms: Windows
Defense Bypassed: Anti-virus, Application control
Version: 1.1
Created: 14 January 2020
Last Modified: 18 October 2021

Procedure Examples

ID Name Description
S0386 Ursnif

Ursnif has injected code into target processes via thread local storage callbacks.[2][3][4]


ID Mitigation Description
M1040 Behavior Prevention on Endpoint

Some endpoint security solutions can be configured to block some types of process injection based on common sequences of behavior that occur during the injection process.


ID Data Source Data Component
DS0009 Process OS API Execution
Process Access
Process Modification

Monitoring Windows API calls indicative of the various types of code injection may generate a significant amount of data and may not be directly useful for defense unless collected under specific circumstances for known bad sequences of calls, since benign use of API functions may be common and difficult to distinguish from malicious behavior. Windows API calls such as CreateRemoteThread, SuspendThread/SetThreadContext/ResumeThread, and those that can be used to modify memory within another process, such as VirtualAllocEx/WriteProcessMemory, may be used for this technique.[5]

Analyze process behavior to determine if a process is performing actions it usually does not, such as opening network connections, reading files, or other suspicious actions that could relate to post-compromise behavior.