t1027-006-html-smuggling

name	T1027.006_html-smuggling
description	Adversaries may smuggle data and files past content filters by hiding malicious payloads inside of seemingly benign HTML files.
category	configuration
version	18.1
author	cyberstrike-official
tags	["mitre-attack","enterprise","t1027.006","defense-evasion","windows","linux","macos","sub-technique"]
technique_id	T1027.006
tactic	defense-evasion
all_tactics	["defense-evasion"]
platforms	["Windows","Linux","macOS"]
mitre_url	https://attack.mitre.org/techniques/T1027/006
tech_stack	["windows","linux","macos"]
cwe_ids	["CWE-693"]
chains_with	["T1027","T1027.001","T1027.002","T1027.003","T1027.004","T1027.005","T1027.007","T1027.008","T1027.009","T1027.010","T1027.011","T1027.012","T1027.013","T1027.014","T1027.015","T1027.016","T1027.017"]
prerequisites	["T1027"]
severity_boost	{"T1027":"Chain with T1027 for deeper attack path","T1027.001":"Chain with T1027.001 for deeper attack path","T1027.002":"Chain with T1027.002 for deeper attack path"}

T1027.006 HTML Smuggling

Sub-technique of: T1027

High-Level Description

Adversaries may smuggle data and files past content filters by hiding malicious payloads inside of seemingly benign HTML files. HTML documents can store large binary objects known as JavaScript Blobs (immutable data that represents raw bytes) that can later be constructed into file-like objects. Data may also be stored in Data URLs, which enable embedding media type or MIME files inline of HTML documents. HTML5 also introduced a download attribute that may be used to initiate file downloads.

Adversaries may deliver payloads to victims that bypass security controls through HTML Smuggling by abusing JavaScript Blobs and/or HTML5 download attributes. Security controls such as web content filters may not identify smuggled malicious files inside of HTML/JS files, as the content may be based on typically benign MIME types such as text/plain and/or text/html. Malicious files or data can be obfuscated and hidden inside of HTML files through Data URLs and/or JavaScript Blobs and can be deobfuscated when they reach the victim (i.e. Deobfuscate/Decode Files or Information), potentially bypassing content filters.

For example, JavaScript Blobs can be abused to dynamically generate malicious files in the victim machine and may be dropped to disk by abusing JavaScript functions such as msSaveBlob.

Kill Chain Phase

• Defense Evasion (TA0005)

Platforms: Windows, Linux, macOS

What to Check

• Identify if HTML Smuggling technique is applicable to target environment
• Check Windows systems for indicators of HTML Smuggling
• Check Linux systems for indicators of HTML Smuggling
• Check macOS systems for indicators of HTML Smuggling
• Verify mitigations are bypassed or absent (1 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: HTML Smuggling Remote Payload

The HTML file will download an ISO file from T1553.005 without user interaction. The HTML file is based off of the work from