Expack Continues Exploiting Java Vulnerability
Exploit kits available in the wild tend to follow a trend by exploiting vulnerabilities reported in various browser components which are commonly deployed. Recently, we have seen an increase in exploitation of a year old vulnerability reported in the JRE component of JAVA (CVE-2012-1723). Exploitation of this vulnerability in JRE allows a attacker to download malware onto a victim's machine and execute it. Let's looks at an analysis of such an exploit kit recently found in the wild.
The applet is executed by the browser, which then downloads a malicious .jar file from following URL,This .jar files exploits the vulnerability in the JRE, which allows the attacker to download additional malware and execute it the browser context.A Trojan then connects to the CnC server by sending POST data and in response, the CnC server replies with 'STATUS-IMPORT-OK'.
Exploit Kit URL:
Obfuscated source code:
Let's take a look at following de-obfuscated code which loads malicious applet into browser:
The following code calls the relevant functions above, depending upon the JRE version found on the victim's machine:
The applet is executed by the browser, which then downloads a malicious .jar file from following URL,
The de-complied code of the downloaded .jar file is also heavily obfuscated.
VT Result: 13 / 45
VT Result: 13 / 46
After receiving command 'STATUS-IMPORT-OK' from the CnC server, The Trojan then downloads another malware file (6.exe) from the same domain which looks to be a variant of ZerooAccess rootkit. The detection rate for the '6.exe' is also fairly low on VT.
VT-Result: 6 / 46
Exploitation of browser components such as Java and Adobe plugins by exploit kits are now a very common reason for enterprise PCs to become compromised. My colleague Krishanan Subramanian recently blogged about a rise in Red Kit Exploit Kit Activity, which also addressed the same vulnerability in Java. It is vital that enterprises ensure that browser plugins are always patched and up to date, something enterprises regularly fail to do. In the case Java, given the now regular stream of 0days that it has inspired, you may want to seriously consider disabling Java altogether, at least at the browser level, something that you can read about in a previous blog post entitled: Are you vulnerable to yet another Java 0Day exploit?