Loading AttackTrace...
Loading AttackTrace...
HTML Smuggling (T1027.006) is a MITRE ATT&CK technique associated with Stealth . Adversaries may smuggle data and files past content filters by hiding malicious payloads inside of seemingly benign HTML files.
HTML Smuggling (T1027.006) is a MITRE ATT&CK technique associated with Stealth. Adversaries may smuggle data and files past content filters by hiding malicious payloads inside of seemingly benign HTML files.
Attackers use HTML Smuggling because it provides a reliable way to advance their objective within the Stealth tactic, often with a favorable balance of impact versus detectability on Linux, macOS, Windows environments. Defenders should assess this behavior in the context of the affected platform and adjacent activity rather than treating it as a standalone indicator.
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.(Citation: HTML Smuggling Menlo Security 2020)(Citation: Outlflank HTML Smuggling 2018)
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 <code>text/plain</code> and/or <code>text/html</code>. 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 <code>msSaveBlob</code>.(Citation: HTML Smuggling Menlo Security 2020)(Citation: MSTIC NOBELIUM May 2021)(Citation: Outlflank HTML Smuggling 2018)(Citation: nccgroup Smuggling HTA 2017)
No universal command represents HTML Smuggling. Capture the exact command line, arguments, parent process, account, host, and execution time from the investigated environment; do not operationalize unverified examples.
| Event ID | Log Channel | What It Indicates |
|---|---|---|
| Environment-specific | Relevant Windows channel(s) | Correlate authentication, process, object-access, and configuration events with the observed execution context. |
| Sysmon Event ID | Name | Why It's Relevant Here |
|---|---|---|
| Environment-specific | Validate configured telemetry | Use process, network, file, registry, DNS, or image-load telemetry only when relevant and enabled. |
No MITRE detection guidance published for this technique.
Relevant ATT&CK Data Sources: N/A
A universal Sigma rule would create unreliable results because this technique has no single guaranteed observable. Build detection logic from a documented behavior and supported data source, scope it to the affected platform, and validate it against benign administrative activity before deployment.
Start with the data sources named in the detection section. Scope searches by asset, identity, and time window; correlate the primary behavior with preceding access and subsequent actions. A portable query is intentionally not provided where the technique lacks a universal schema or observable.