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Safer Internet

Anna is the director of a small kindergarten in Zurich. To give the kindergarten a home on the Internet, she registered a domain name and put up a website where parents can get up-to-date information about the kindergarten. A friend helped her to install a popular open-source content management system (CMS) for the website, so that she can change the menu every week and perform other updates herself. The parents of the kids were delighted to have access to this information online.

Three months after the website went online, one of the parents called her, telling her that the website was no longer available, and a warning was displayed instead. He also told her that he had a virus on his home PC and had to reinstall his operating system and change all his Internet passwords. When she talked to other parents that day, they told her the same.

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So Long, and Thanks for All the Domains

While Trojans like Dyre and Dridex are dominating malware-related news, we take the time to have a closer look at Tinba (Tiny Banker, Zusy, Illi), yet another Trojan which targets Windows users. In the first part of this post, we give a short historical review, followed by hints about how to detect (and remove) this threat on an infected system. In the second part, we have a look at a portion of the Trojan’s code which enhances its communication resilience, and how we can leverage these properties for defensive purposes.

Tinba is a fine piece of work, initially purely written in assembly. CSIS discovered it back in May 2012, and it contained WebInject capability and rootkit functionality in a binary of just 20 KB. The source code of Tinba leaked in July 2014, helping bad guys to create their own, extended versions.

Tinba Rootkit ZwQueryDirectoryFile

The source code of Tinba leaked in July 2014. Shown are some preparations to hook ZwQueryDirectoryFile.

Tinba on steroids was discovered in September 2014. Two main features are worth noting: First, each binary comes with a public key to check incoming control messages for authenticity and integrity. Second, there is a domain generation algorithm (DGA), which we will discuss later. In October 2014, Tinba entered Switzerland, mainly to phish for credit card information.

Tinba Inject

Tinba tried to phish credit card information.

Like other commodity Trojans, Tinba checks whether it is running in a virtual machine/sandboxed environment by checking the hard-disk size or looking for user interaction. According to abuse.ch, there was an intense distribution of Tinba in Switzerland early this year. Such spam campaigns can happen again at any time, so it is of use to know how to detect Tinba on an infected system and remove it.

Even though Tinba has the ability to hide directories and files (rootkit functionality), cybercriminals were wondering why they should bother using it. Why not simply hide directories and files with the “hidden” flag, which works for most users? Thus, it is relatively simple for a computer-savvy user to remove this version of Tinba from an infected (see instructions below).

Tinba Directory Hidden

A randomly named directory, which contains the Trojan itself, can be hidden by setting its attributes to “hidden”.

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Protect your network with DNS Firewall

If you run your own mail server, you will quickly find out that 90% of the e-mails you receive are spam. The solution to this problem is e-mail filtering, which rejects or deletes unwanted spam. This solution is generally well accepted, and most users would not want the old days back when your inbox was filled with scams. Those people who want spam can also work around it by disabling spam filtering for their e-mail address or opting to run their own mail server.

Spam, scammers and other malicious abuse are not unique to e-mail. One possible approach is to invent a filtering technology for every protocol or service and allow the service owners to block misuse according to their policy. On the other hand, most services on the Internet make use of the Domain Name System (DNS). If you control DNS name resolution for your organisation, you can filter out the bad stuff the same way you filter out spam on e-mail. The difference and the advantage of DNS is that DNS filtering is independent of the service you use.

Back in 2010, ISC and Paul Vixie invented a technology called Response Policy Zones (RPZ) (See CircleID Post Taking back the DNS). While it has always been possible to block certain domain names from being resolved on your DNS resolver, adding host names manually as an authoritative zone does not scale.

(Illustration Christoph Frei)

(Illustration Christoph Frei)

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Drive-by code and Phishing on Swiss websites in 2014

In 2014, about 1,800 Swiss websites were cleaned from drive-by code, compared with 2,700 in 2013, a decline of 33%. At the same time, the number of phishing cases affecting .ch and .li top-level domains rose from only a handful in 2013 to more than 300.

Drive-by code on Swiss websites in 2014

Last year, 35,796 suspicious drive-by URLs in the .ch and .li top-level domains were reported to SWITCH. Security experts from SWITCH-CERT automatically sent requests to these servers and analysed the responses, looking for malicious code injected into the HTML source code. When an expert identified malicious code, the registrar or domain name holder and the web hoster were notified and asked to remove it within one working day. This was done for 1,839 domain names in 2014. In 1,493 (81%) cases, the code was removed by the web hoster or domain holder within one day. For the other 346 domains, the deadline was not met, and the domain name was temporarily suspended to prevent further damage to website visitors. Some 264 (14%) of the infected websites were cleaned of malicious code, with the remaining 82 domain names having to be reactivated after five days, the maximum suspension time by law. A request for identification was sent to the holders of all 82 domains, resulting in an additional 59 (3.2%) of websites being cleaned. A total of 23 (1.3% of all notified) domain names were deleted after 30 days because the domain holder failed to respond to the identification request.

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Compromised .ch and .li websites used for drive-by infections by quarter

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A look at a phishing website

Yesterday we came across a phishing website under .ch where we were able to download the phishing kit. A phishing kit is an archive file which contains all the relevant files for hosting a phishing website. In this case, the archive contained some static HTML, JS and image files for hosting the phishing form, but also a PHP file for sending the data to the perpetrator, and – most interestingly –an .htaccess file. The .htaccess file is a configuration file used by some popular web servers, which allows the user of a website to override a subset of the server’s global configuration for the directory that the file is located in and all its sub-directories.

A phishing website is frequently only accessible from the targeted country. In our case, this was controlled by the .htaccess file which contained a large list of IP address ranges from where it is allowed to access the site. As an incident handler, we often get reports of malicious websites that we cannot verify with IP addresses from Swiss ISPs. An unwary user might think that the phishing website has already been taken down, but that is not the case. The user is just not allowed to access the phishing website from its IP address.

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IT-Security-Links #21