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:


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://, IE interprets the mhtml request for multipart/related content and sends a normal GET request to the server as After receiving the response back it again prefixes with mhtml as mhtml:

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.


Popular posts from this blog

File Upload through Null Byte Injection

Sometimes, during file upload we come across situation wherein there would be check on the file extension at the client side as well as server side too. If the application does allow only .jpeg extension to be uploaded, the client side java script checks for the extension of the file before passing the request. We all know that how easily this can be defeated.
Some applications, checks for the extension at the server side also. That's not easy to bypass. However there are some ways with which it still can be bypassed. Most of server side scripts are written in high level languages such as Php, Java etc who still use some C/C++ libraries to read the file name and contents. That leads to the problem. In C/C++ a line ends with /00 or which is called Null Byte. So whenever the interpreter sees a null byte at the end of the a string, it stops reading thinking it has reached at the end of the string.
This can be used for the bypass. It works for many servers, specially php servers. Th…

SQL Injection in search field

Earlier I had written about performing SQL injection in search field and how to do a DoS attack and privilege escalation using 'Like' operators. Now another SQLi exploitation I came across recently. That too in the search field. This becomes important as lots of people don't pay much attention on the search forms/ fields in the application. My aim is to show that a search form can also be exploited with SQL Injection. The following queries are based on a real world exploitation. The steps and data are for just illustration purpose only. Suppose, the search form provides the details of users who have accessed the application some time and their login time details etc, we just need to provide their name in the search box provided. All the data were being going as Post request. So, to just fingerprint the database, I provide, 'nil'+'esh' in the search field and it successfully gives me the results. That means the database behind the application is concatenat…

Insecure protocols

Some basic insecure protocols and risk associated with them: