Event Triggered Execution: Image File Execution Options Injection

Adversaries may establish persistence and/or elevate privileges by executing malicious content triggered by Image File Execution Options (IEFO) debuggers. IEFOs enable a developer to attach a debugger to an application. When a process is created, a debugger present in an application’s IFEO will be prepended to the application’s name, effectively launching the new process under the debugger (e.g., C:\dbg\ntsd.exe -g notepad.exe). [1]

IFEOs can be set directly via the Registry or in Global Flags via the GFlags tool. [2] IFEOs are represented as Debugger values in the Registry under HKLM\SOFTWARE{{\Wow6432Node}}\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\ where <executable> is the binary on which the debugger is attached. [1]

IFEOs can also enable an arbitrary monitor program to be launched when a specified program silently exits (i.e. is prematurely terminated by itself or a second, non kernel-mode process). [3] [4] Similar to debuggers, silent exit monitoring can be enabled through GFlags and/or by directly modifying IEFO and silent process exit Registry values in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SilentProcessExit\. [3] [4]

Similar to Accessibility Features, on Windows Vista and later as well as Windows Server 2008 and later, a Registry key may be modified that configures "cmd.exe," or another program that provides backdoor access, as a "debugger" for an accessibility program (ex: utilman.exe). After the Registry is modified, pressing the appropriate key combination at the login screen while at the keyboard or when connected with Remote Desktop Protocol will cause the "debugger" program to be executed with SYSTEM privileges. [5]

Similar to Process Injection, these values may also be abused to obtain privilege escalation by causing a malicious executable to be loaded and run in the context of separate processes on the computer. [6] Installing IFEO mechanisms may also provide Persistence via continuous triggered invocation.

Malware may also use IFEO to Impair Defenses by registering invalid debuggers that redirect and effectively disable various system and security applications. [7] [8]

ID: T1546.012
Sub-technique of:  T1546
Tactics: Privilege Escalation, Persistence
Platforms: Windows
Permissions Required: Administrator, SYSTEM
Data Sources: API monitoring, Process command-line parameters, Process monitoring, Windows Registry, Windows event logs
Contributors: Oddvar Moe, @oddvarmoe
Version: 1.0
Created: 24 January 2020
Last Modified: 24 March 2020

Procedure Examples

Name Description
SDBot

SDBot has the ability to use image file execution options for persistence if it detects it is running with admin privileges on a Windows version newer than Windows 7.[9]

TEMP.Veles

TEMP.Veles has modified and added entries within HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options to maintain persistence.[10]

Mitigations

This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.

Detection

Monitor for abnormal usage of the Glfags tool as well as common processes spawned under abnormal parents and/or with creation flags indicative of debugging such as DEBUG_PROCESS and DEBUG_ONLY_THIS_PROCESS. [1]

Monitor Registry values associated with IFEOs, as well as silent process exit monitoring, for modifications that do not correlate with known software, patch cycles, etc. Monitor and analyze application programming interface (API) calls that are indicative of Registry edits such as RegCreateKeyEx and RegSetValueEx. [6]

References