T1221 Template Injection

T1221 Template Injection

High-Level Description

Adversaries may create or modify references in user document templates to conceal malicious code or force authentication attempts. For example, Microsoft’s Office Open XML (OOXML) specification defines an XML-based format for Office documents (.docx, xlsx, .pptx) to replace older binary formats (.doc, .xls, .ppt). OOXML files are packed together ZIP archives compromised of various XML files, referred to as parts, containing properties that collectively define how a document is rendered.

Properties within parts may reference shared public resources accessed via online URLs. For example, template properties may reference a file, serving as a pre-formatted document blueprint, that is fetched when the document is loaded.

Adversaries may abuse these templates to initially conceal malicious code to be executed via user documents. Template references injected into a document may enable malicious payloads to be fetched and executed when the document is loaded. These documents can be delivered via other techniques such as Phishing and/or Taint Shared Content and may evade static detections since no typical indicators (VBA macro, script, etc.) are present until after the malicious payload is fetched. Examples have been seen in the wild where template injection was used to load malicious code containing an exploit.

Adversaries may also modify the *\template control word within an .rtf file to similarly conceal then download malicious code. This legitimate control word value is intended to be a file destination of a template file resource that is retrieved and loaded when an .rtf file is opened. However, adversaries may alter the bytes of an existing .rtf file to insert a template control word field to include a URL resource of a malicious payload.

This technique may also enable Forced Authentication by injecting a SMB/HTTPS (or other credential prompting) URL and triggering an authentication attempt.

Kill Chain Phase

• Defense Evasion (TA0005)

Platforms: Windows

What to Check

• Identify if Template Injection technique is applicable to target environment
• Check Windows systems for indicators of Template Injection
• Verify mitigations are bypassed or absent (4 known mitigations)
• Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: WINWORD Remote Template Injection

Open a .docx file that loads a remote .dotm macro enabled template from https://github.com/redcanaryco/atomic-red-team/tree/master/atomics/T1221/src/opencalc.dotm Executes the code specified within the .dotm template. Requires download of WINWORD found in Microsoft Ofiice at Microsoft: https://www.microsoft.com/en-us/download/office.aspx.
Default docs file opens Calculator.exe when test sucessfully executed, while AV turned off.