Skip to main content

MHTML files

Today my colleague Surendra had a query regarding a weird popup coming up while he was trying to access a website. Although even, I was not very familiar with the kind of message he was getting. All we wanted to know, if it's really anything malicious! He was trying to access some page, and the website was making some weird request to the webserver in order to load some object (here it was a calender) from the server:

mhtml:http://abc.com/resources/Calnder.mht

The warning message was like this:

Even I had not noticed like anything in the past, I did a little research on the topic. The browser was trying to load some MHTML page.MHTML is simply a MIME HTML format, used to combine all the external resources, which are generally loaded as external link, with HTML code into a single file. Generally this file has extension as .mht. So any .mht file contains mix of HTML code and other objects such as, Flash, images, applets, audio files etc. The content of .mht file is encoded in base64. (Wiki)

So when you are requesting a .mht file it will be loaded into multipart one-by-one, as the file may be large. Also, to minimize the lots of GET requests to server, it can be used. So IE uses mhtml:http:// format to request such type of files from the server. But again IE strips the mhtml part and makes the normal GET request to the web server. Again when it gets the response from the server again it prefixes the mhtml before it. So for example, if you request mhtml://http://abc.com/anyFile.mht, IE interprets the mhtml request for multipart/related content and sends a normal GET request to the server as http://abc.com/anyFile.mht. After receiving the response back it again prefixes with mhtml as mhtml:http://abc.com/anyFile.mht.

So, regarding his case, there was some script injection vulnerability with the way the Windows treats the MHTML long ago. So, Microsoft came up with a lock-down solution for the MHTML being used in the URL. Now you can’t use mhtml in urls/hyperlinks if that fix is applied on the server. But still MHTML can works behind the scene, the only thing is you can never request it as mhtml:http://. Generally .mht doesn’t contain script but if it contains that and the lock-down for the MHTML is applied on the server, it pops-up a message like you faced: “This webpage is trying to communicate with your computer using a protocol that your security setting don’t allow”. You can simply allow the pop-up by clicking yes to be rendered option. No harm in that.

So in his case, it may be the browser is trying to access some url in the mhtml:http:// format and mhtml have been locked down on the remote server or in your IE settings, that could be a reason you are getting the pop-up alert.

Again, all the above observations are based on my google, might not be 100% correct, but one might have got the picture a bit. So nothing malicious in that request.

Comments

Post a Comment

Popular posts from this blog

Using an AirPcap device in Windows with Wireshark

Capturing wireless traffic in a Windows environment is unfortunately not as easy as a setting change. As with most Windows-based software, drivers in Windows are often not open source and do not allow for configuration change into monitor mode. With this in mind, we must use a specialized piece of hardware known as an AirPcap device. Once you have obtained an AirPcap device you will be required to install the software on the accompanying CD to your analysis computer. The configurable options include: • Interface - Select the device you are using for your capture here. Some advanced analysis scenarios may require you to use more than one AirPcap device to sniff simultaneously on multiple channels. • Blink LED - Clicking this button will make the LED lights on the AirPcap device blink. This is primarily used to identify the specific adapter you are using if you are using multiple AirPcap devices. • Channel - In this field, you select the channel you want AirPcap to listen on. Extension C...
5 comments
Read more

Anti CSRF header

Recently I came across an application which was preventing crsf attacks using a unique non-traditional approach. In traditional approach the csrf is thwarted by embedding unique random tokens, called nonce, in each sensitive page. But this application, which was making ajax calls and used jQuery, was creating a header to identify the valid and invalid requests altogether. The idea is to generate a custom header, x-session-token in this case, with every request which is considered sensitive and includes any sort of transaction. For example: xhr.setRequestHeader('x-session-token', csrf_token)   At the server level, server checks for this header if found request is fulfilled, otherwise rejected. We need to use xhr calls for making use of this technique, not useful in regular POST and GET requests. Since, I was not aware of this kind of countermeasures, probably, since most of the applications I did were using standard requests. So, I searched a bit and found even Go...
4 comments
Read more

Some one watching where you visited!

Yes... Mozilla has been susceptible to browser-history stealing java script code. Today, Giorgio posted some cool information about the exploit. Mozilla is already working on this. This bug has been reported. Actually they have set up a web site to show the proof-of-concept. Visit www.statrpanic.com in FF,Safari or Netscape and it will tell you which websites have you been already ! But I am not sure it will work in IE or not because my IE is not responding to the website. Clearing history of visited website makes you safe to this attack. I mean this is one way..may be there are other ways to exploit this. But I have found this effective. Try it yourself in FF and then in IE and see the results.
Post a Comment
Read more