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.[1],[2]
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.[1],[3],[2],[4]
References
- Subramanian, K. (2020, August 18). New HTML Smuggling Attack Alert: Duri. Retrieved May 20, 2021.
- Hegt, S. (2018, August 14). HTML smuggling explained. Retrieved May 20, 2021.
- Microsoft Threat Intelligence Center (MSTIC). (2021, May 27). New sophisticated email-based attack from NOBELIUM. Retrieved May 28, 2021.
- Warren, R. (2017, August 8). Smuggling HTA files in Internet Explorer/Edge. Retrieved September 12, 2024.
Kwistjonijiet marbuta
| Tip ta’ link | Kwistjoni |
|---|---|
| is related to | Techniques |
| is blocked by | Application Isolation and Sandboxing |
| is blocked by | Detection Strategy for HTML Smuggling via JavaScript Blob + Dynamic File Drop |
- MITREATTACK -
© 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation. https://attack.mitre.org/
Terms of Use
LICENSE
The MITRE Corporation (MITRE) hereby grants you a non-exclusive, royalty-free license to use ATT&CK® for research, development, and commercial purposes. Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy.
"© 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation."
DISCLAIMERS
MITRE does not claim ATT&CK enumerates all possibilities for the types of actions and behaviors documented as part of its adversary model and framework of techniques. Using the information contained within ATT&CK to address or cover full categories of techniques will not guarantee full defensive coverage as there may be undisclosed techniques or variations on existing techniques not documented by ATT&CK.
ALL DOCUMENTS AND THE INFORMATION CONTAINED THEREIN ARE PROVIDED ON AN "AS IS" BASIS AND THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE MITRE CORPORATION, ITS BOARD OF TRUSTEES, OFFICERS, AGENTS, AND EMPLOYEES, DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
See our FAQ for more information on how to use and represent the ATT&CK name.