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Gadi Evron and Tillmann Wernerpresented an interesting case at 31C3 Conference in Hamburg yesterday, that shows how commercial software can be used to launch APT style attacks. In this case, several similar attacks where discovered against targets in Israel and Western Europe. In all cases, the attack started with a simple Excel spreadsheet which was sent as an attachment[1]. The email itself was brief and unremarkable, but used fake and plausible From headers.

Gadi was nice enough to share with us some screenshots of these attachments. They are all very plausible for the targeted recipients. Click on the thumbnail to see the full size image (these are images, not the original Excel files)

Screenshots of Excel E-Mail Attachments

Each Excel file included a macro.While the use of Excel Macros and the simple e-mail message initially looked like an old and simple exploit, thebackdoor caught the attention of Gadi and Tillmannwho assisted with the reverse analysis. It turned out more sophisticated and stealthy then what was found in standard crimeware.

The Excel macro consisted of two files. One was an encodedPE binary, the second a simple VBA script to decode the PE binary, write it to disk and run it. This binary is where things got more interested. It implemented a very capable backdoor, essentially proxyingsystem calls, allow for very flexible access to the system not limiting the attacker to aset of pre-defined commands.

In the end, it turned out that the entire attack was performed using Core Impact, a pricey, but highly sophisticated product allowing for point and click attacks of a level that are typically used for APT attacks [2]. In particular when attributing attacks like this to Nation States, or suggesting that the attacker has to be highly sophisticated and able to write custom exploits, one has to consider the possibility that the attacker just re-purposed commercial pentesting software like Core Impact, or even open source tools that offer similar features. The budget for such an attack typically is well below $100kto purchase the required software, a number that is well within reach of even minor nations or organized crime groups. In some cases, it may be possible to find pirated copies fo the required software. Another advantage of using commercial software is the ability to ask for support or professional services to help you with your APT attack.

Oddly, the backdoor was not recognized by anti-virus tools, even though Core Impactis a commonly used product. Core impact also fails to tag any of the software with a customer specific serial number, hindering attribution in cases like the one above. Such a serial number would not prevent an authorized pen test, but would help attribute unauthorized attacks.

For more details, I highly recommend that you watch Gadi and Tillmann[1].

[1]http://streaming.media.ccc.de/relive/6575/ (The talk starts around 15 min into the recording)

Indicators of compromise:

IP Addresses


MD5 Hashes



/> Johannes B. Ullrich, Ph.D.

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