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AAn '''HTML Application''' ('''HTA''') is a [[Microsoft Windows]] program whose source code consists of [[HTML]], [[Dynamic HTML]], and one or more scripting languages supported by [[Internet Explorer]], such as [[VBScript]] or [[JScript]]. The HTML is used to generate the user interface, and the scripting language is used for the program logic. AAn HTA executes without the constraints of the internetweb browser security model; in fact, it executes as a "fully trusted" application.
The usual file extension of aan HTA is <code>.hta</code>.
The ability to execute HTAs was introduced to Microsoft Windows in 1999, along with the release of [[Microsoft Internet Explorer 5]].<ref>[http://support.microsoft.com/kb/200874 ''Article ID:200874 in Microsoft Support''], in Microsoft Support Knowledge Base</ref> On December 9, 2003, this technology was [[patent]]ed.<ref>[http{{Cite patent|number=US6662341B1|title=Method and apparatus for writing a windows application in HTML|gdate=2003-12-09|invent1=Cooper|invent2=Kohnfelder|invent3=Chavez|inventor1-first=Phillip R.|inventor2-first=Loren M.|inventor3-first=Roderick A.|url=https://newspatents.cnetgoogle.com/2100patent/US6662341B1/en?oq=PN/6,662,341}}</ref><ref>{{Cite web |last=Festa |first=Paul |date=2003-1012_312-5119072.html10 |title=Microsoft wins HTML application patent |url=http://www.cnet.com/news/microsoft-wins-html-application-patent/ |url-status=dead |archive-url=https://web.archive.org/web/20160310170211/http://www.cnet.com/news/microsoft-wins-html-application-patent/ |archive-date=2016-03-10 |access-date=2016-01-10 |website=[[CNET]]}}</ref>
== Uses ==
===Execution===
[[File:RectifiedWikipediaHTAWindow.png|alt=|thumb|346x346px|One screenshot of one example window that is produced by <code>mshta.exe</code>]]
AAn HTA is executed using the program <code>mshta.exe</code>, or, alternatively, double-clicking on the file. This program is typically installed along with Internet Explorer. <code>mshta.exe</code> executes the HTA by instantiating the Internet Explorer rendering engine (mshtml) as well as any required language engines (such as vbscript.dll).
AAn HTA is treated like any executable file with extension [[EXE|<code>.exe</code>]]. When executed via mshta.exe (or if the file icon is double-clicked), it runs immediately. When executed remotely via the browser, the user is asked once, before the HTA is downloaded, whether or not to save or run the application; if saved, it can simply be run on demand after that.<ref name=msintro/>
By default, HTAs are rendered as per "standards-mode content in IE7 Standards mode and quirks mode content in IE5 (Quirks) mode", but this can be altered using <code>X-UA-Compatible</code> headers.<ref name=msintro>{{cite web |url=https://msdn.microsoft.com/en-us/library/ms536496%28v=vs.85%29.aspx#Compatibility |title=Introduction to HTML Applications (HTAs).|website=MicrosftMicrosoft MSDN|date=May 2011 |access-date= 24 June 2016}} Sections include Why Use HTAs, Creating aan HTA, HTA-Specific Functionality, Security, Compatibility, Deployment</ref>
HTAs are dependent on the Trident (MSHTML) browser engine, used by [[Internet Explorer]], but are not dependent on the Internet Explorer application itself. If a user [[Removal of Internet Explorer|removes Internet Explorer]] from Windows, via the Control Panel, the MSHTML engine remains and HTAs continue to work. HTAs continue to work in Windows 11 as well.
When a regular HTML file is executed, the execution is confined to the security model of the [[web browser]]. This means it is confined to communicating with the server, manipulating the page's [[object model]] (usually to validate forms and/or create interesting visual effects) and reading or writing [[HTTP cookie|cookies]].
On the other hand, aan HTA runs as a fully trusted application and therefore has more privileges than a normal HTML file; for example, aan HTA can create, edit and remove files and [[Windows Registry|registry]] entries. Although HTAs run in this 'trusted' environment, querying [[Active Directory]] can be subject to Internet Explorer Zone logic and associated error messages.
==Development==
To customize the appearance of aan HTA, an optional tag <code>hta:application</code> was introduced to the <code>HEAD</code> section. This tag exposes a set of attributes that enable control of border style, the program icon, etc., and provide information such as the argument (command line) used to launch the HTA.<ref>[https://msdn.microsoft.com/en-us/library/aa360681(v=VS.85).aspx ''HTA:APPLICATION Object''], in MSDN Library, the complete specification of the tag <code>hta:application</code></ref> Otherwise, aan HTA has the same format as aan HTML page.
Any text editor can be used to create aan HTA. Editors with special features for developing HTML applications may be obtained from Microsoft<ref>[http://www.microsoft.com/downloads/details.aspx?FamilyId=231D8143-F21B-4707-B583-AE7B9152E6D9&displaylang=en ''HTA Helpomatic'']</ref> or from third-party sources.<ref>[http://www.htaedit.com/ ''HTAEdit, an editor for HTAs with a built-in debugger'']</ref>
An existing HTML file (with file extension <code>.htm</code> or <code>.html</code>, for example) can be changed to aan HTA by simply changing the extension to <code>.hta</code>.
==Vulnerabilities==
HTA have been used to deliver malware.<ref>{{Cite web|url=https://www.vmray.com/cyber-security-blog/spora-ransomware-dropper-hta-infect-system/|title=Spora Ransomware Dropper Uses HTA to Infect System|date=2017-01-17|website=VMRay|language=en-US|access-date=2018-12-22}}</ref><ref>{{Cite web|url=https://blog.netwrix.com/2017/06/01/nine-scariest-ransomware-viruses/|title=8 Scariest Ransomware Viruses|language=en-US|access-date=2018-12-22}}</ref> One particular HTA, named ''[[4chan]].hta'' (detected by antiviruses as JS/Chafpin.gen), was widely distributed by the users of the imageboard as a [[steganographic]] image in which the user were instructed to download the picture as aan HTA file, which when executed, would cause the computer to automatically spam the website (evading 4chan's [[CAPTCHA]] in the process) with alternate variants of itself; it was reported that such attacks were previously delivered in which the user was prompted to save it as a [[JavaScript|.js]] file.<ref>{{cite web |last1=Constantin |first1=Lucian |title=4chan Flood Script Is Back with New Social Engineering Trick |url=https://news.softpedia.com/news/4chan-Flood-Script-Is-Back-with-New-Social-Engineering-Trick-151603.shtml |website=Softpedia |access-date=2021-11-09 |date=2010-08-10}}</ref>
==Example==
This is an example of [["Hello, World!" program|Hello World]] as aan HTML Application.
<syntaxhighlight lang="html4stricthtml">
<HTML>
<HEAD>
==External links==
* [http://msdn2.microsoft.com/en-us/library/ms531018.aspx HTML Component (HTC) Reference at MSDN]. AAn HTC encapsulates specific functionality or behavior within HTAs.
* [https://technet.microsoft.com/en-ca/scriptcenter/default.aspx The Script Center], The Script Center, home of Hey, Scripting Guy! Blog
* [https://technet.microsoft.com/en-ca/scriptcenter/dd742317.aspx Learn About Scripting for HTML Applications (HTAs)], a tutorial site for learning about HTA's
{{Internet Explorer}}
[[Category:HTML|Application]]
[[Category:Internet Explorer]]
[[Category:User interface markup languages]]
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