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This File Appears To Be Malicious, Google Chrome Safe Browsing Protection

Martin Brinkmann — Wed, 06 Apr 2011 09:35:43 +0000

Chrome users on the developer channel or Canary will see download warnings if they try to download a file on a website that matches the list of malicious websites published by Google’s Safe Browsing Api. The warning reads “This file appears to be malicious. Are you sure you want to continue” with options to discard and save. The options may cause quite the confusion among users, and it would probably have been better if Google would have simply added Yes and No buttons to the prompt

Another thing to remember is that all downloads of said websites will be flagged, regardless whether they are indeed malicious or dangerous in nature, or not. All downloads? Well that is not entirely right, at least not for now. Google flags all Windows executable downloads as suspicious if the site is on the Safe Browsing list. No warning is currently displayed for other files. These files are not actually scanned by Google, keep that in mind if the warning message pops up.

Safe Browsing is used by Google Search, and various web browsers to warn users when they visit web pages or sites that have been flagged.

Safe Browsing has done a lot of good for the web, yet the Internet remains rife with deceptive and harmful content. It’s easy to find sites hosting free downloads that promise one thing but actually behave quite differently. These downloads may even perform actions without the user’s consent, such as displaying spam ads, performing click fraud, or stealing other users’ passwords. Such sites usually don’t attempt to exploit vulnerabilities on the user’s computer system. Instead, they use social engineering to entice users to download and run the malicious content.

The feature has already been implemented into Google Chrome dev and Canary, and Google plans to release it at a later time for the beta and stable branches as well. It is not clear yet if Linux and Mac users will see the warning messages as well, chance is they will. (via)

NTFS Alternate Data Streams

Martin Brinkmann — Thu, 24 Jan 2008 16:51:55 +0000

This article is going to explain NTFS Alternate Data Streams: what they are, where they are, how you can detect them, create them and how they are used by hackers. In short, NTFS Alternate Data Streams can be used by hackers to fork file data into existing files without altering the existing file’s function or size. You can guess where this is going, right ? They make it relatively easy to hide malicious code inside them which is much harder to detect.

Creating NTFS Alternate Data Streams is not complicated at all. You can use the “type” command to do that. To fork the file virus.exe into calc.exe you would use the command type virus.exe > calc.exe:virus:exe if they are in the same directory. Add the path if they are not. The size of the calculator does not change, the only indicator is that the file changed stamp is altered.

But executing those files must be harder, right ? Wrong again. To execute virus.exe you use the command “start”, in our example it would be start calc.exe:virus:exe.

A software like Stream Explorer can find those NTFS Alternate Data Streams on your hard drive. An alternative is List Alternate Data Streams

Cross Site Scripting

Martin Brinkmann — Thu, 27 Oct 2005 18:32:42 +0000

Cross site scripting (also known as XSS) occurs when a web application gathers malicious data from a user. The data is usually gathered in the form of a hyperlink which contains malicious content within it. The user will most likely click on this link from another website, instant message, or simply just reading a web board or email message. Usually the attacker will encode the malicious portion of the link to the site in HEX (or other encoding methods) so the request is less suspicious looking to the user when clicked on. After the data is collected by the web application, it creates an output page for the user containing the malicious data that was originally sent to it, but in a manner to make it appear as valid content from the website.

Many popular guestbook and forum programs allow users to submit posts with html and javascript embedded in them. If for example I was logged in as “john” and read a message by “joe” that contained malicious JavaScript in it, then it may be possible for “joe” to hijack my session just by reading his bulletin board post. Further details on how attacks like this are accomplished via “cookie theft” are explained in detail below.

Source: “The Cross Site Scripting FAQ”. Click link to read the whole faq.

Update: Users who are looking for protection against Cross Site Scripting attacks may want to check out the excellent NoScript add-on for the Firefox web browser. XX protection is automatically enabled after installation. The extension for Firefox blocks untrusted websites from injecting scripts into trusted websites, which is an excellent way of protecting users from XSS attacks.

Additional information about Cross Site Scripting are available on Wikipedia. The external links section on the site is especially useful for researchers and security interested users.