A new Apache exploit discovered and analyzed by Eset injects malware into Web pages on a Web server. The so-called Linux/Chapro.A variant has multiple features to camouflage its presence, and basically "tricks" the unsuspecting Apache software into infecting a visitor's machine, according to Eset's findings.
The malware injects an iFrame onto the server that ultimately leads to the installation of Zeus variant Win32/Zbot. It also links to the so-called Sweet Orange exploit kit landing page, out of Lithuania.
"More than half of all web servers on the Internet use Apache, so when we discovered a malicious Apache module in the wild last month, being used to inject malicious content into web pages displayed by compromised web servers, we were understandably concerned," says Pierre-Marc Bureau, security intelligence program manager at Eset, in a blog posting on the malware.
Linux/Chapro.A injects iFrames by sending an HTTP POST request to its command-and-control server every 10 minutes.
The malware pushes a pop-up message to the banking customer asking for a bank card CVV code: If the user falls for it and provides it, that information as well as banking credentials go to the bad guys.
Just how it all starts is still unclear. "This is a malicious module installed on an otherwise non-malicious server. This implies the controls protecting server access were circumvented or there is an insider involved. However, we also need to consider the module could have been part of a corrupted Linux distribution or application package," Bureau told Dark Reading.
He says Eset doesn't know how the module got onto the server to begin with: "Could be a weak password, vulnerable Web application, etc. The user needs high privileges to load the module so, he most probably had root on the machine," Bureau says.
"We don't know who is spreading this but probably a gang specializing in such attacks, then renting 'traffic' to other groups," he says.
The attack employs multiple stealth modes to mask it from website operators, including checking for known bots and active SSH systems. "If a visitor browses a page using any of the same IPs involved in a SSH connection, it will not be served the malicious content. This helps hide the malicious content from system administrators, Web developers, and others who might be working on the Web server," Bureau says.
Linux/Chapro.A also places a cookie in the visitor's browser before the malware injects the iFrame into the Web content. "Malicious content will not be served if the visiting browser already had that cookie set. This helps ensure that visitors will not receive malicious content over and over again, making it more difficult to determine how a system was infected," he says. And the malware ensures that it only infects a victim once by keeping a list of IP addresses it has infected.
The malware's command-and-control server was hosted in Germany, but since has gone offline.
"This complicated case spreads across three different countries, targeting users from a fourth one, making it very hard for law enforcement agencies to investigate and mitigate," Bureau blogged. "It is not clear at this point in time if the same group of people are behind the whole operation, or if multiple gangs collaborated, perhaps with one to drive traffic to the exploit pack and sell the infected computers to another gang operating a botnet based on Win32/Zbot."
The full Eset blog post is here.
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