Blackhole Exploit Kit Behind USPS Attack

Miscreants attacked one of the Websites belonging to the U.S. Postal Service using the Blackhole Exploit kit to deliver up to nine Trojans customized for the user's system.

Cyber-attackers hacked one of the sites belonging to the U.S. Postal Service to redirect visitors to an attack portal containing Trojans. The attackers used a kit to launch the Javascript attack.

The USPS national customer support center,, was compromised using the Blackhole Exploit Kit, researchers at Zscaler said April 7. Attackers injected malicious Javascript on the USPS site that inserted a redirect code to take users to a different site.

The USPS has taken down the infected site and it appears the page the attackers redirect visitors to is offline as well. As of early April 8, Google still reported the site as "may harm your computer" on its search results page and Firefox flagged it as a "Reported Attack Page."

The initial Javascript code injected on the page was obfuscated as each letter was encoded using its ASCII equivalent. To any user, it looks like a series of numbers enclosed within a <script> tag. Zscaler decoded the code to find it was a redirect to load a Russian domain within an IFRAME.

When the malicious code was executed, by the user clicking on a link, for example, users were redirected to the Russian site that had been injected into the page. That site had another line of Javascript to automatically send the visitors to another site with a Cook Islands domain.

The users never saw the intermediary page, which may have been another legitimate site that had been compromised, Zscaler researchers speculated.

Instead, they saw the final attack portal, which displayed a 404 Page Not Found error message. In actuality, a drive-by-download was running in the background. The obfuscated Javascript script on the attack page, when executed, checked the victim's operating system, browser type, and the state of important software components such as ActiveX and Java. A payload customized to the user's system information and existing unpatched vulnerabilities was downloaded.

There were nine Trojans to choose from, including executable files, malicious PDF files and PHP scripts. The PHP files exploited known Java vulnerabilities. According to Virus Total, none of them would have been detected by most major antivirus programs. Three of the potential downloads - an executable and two malicious PDF files - were the best recognized, with five out of 42 antivirus programs tracked by Virus Total able to detect them.

The Blackhole Exploit kit, a commercial kit developed by Russian developers, has been used in a number of attacks, according to Zscaler. The attack kit used allows individuals with little or no coding knowledge to deliver a hostile payload, whether that is scareware software or something else. A recent Symantec report found that automated attack kits targeting Websites accounted for two-thirds of all Web-based attacks in 2010.

The same Blackhole Exploit was behind the malicious advertisements that appeared on the free version of Spotify last month.

The name of the affected site,, stands for Rapid Information Bulletin Board System. The site handles the postal service's Intelligent Mail services, such as barcode-based tracking for business mail.