by Dennis Fisher - November 20, 2012New Linux Rootkit Emerges
A new Linux rootkit has emerged and researchers who have analyzed its code and operation say that the malware appears to be a custom-written tool designed to inject iframes into Web sites and drive traffic to malicious sites for drive-by download attacks. The rootkit is designed specifically for 64-bit Linux systems, and while it has some interesting features, it does not appear to be the work of high-level programmer or be meant for use in targeted attacks
The new Linux rootkit is loaded into memory and once there, it pulls out some memory addresses and then stores them for use later. It also then hooks into several kernel functions as a way to hide some of its files on the machine.
"To hook private functions that are called without indirection (e.g., through a function pointer), the rootkit employs inline code hooking. In order to hook a function, the rootkit simply overwrites the start of the function with an e9 byte. This is the opcode for a jmp rel32 instruction, which, as its only operand, has 4 bytes relative offset to jump to," Georg Wicherski of CrowdStrike wrote in a detailed analysis of the new Linux malware.
"The rootkit, however, calculates an 8-byte or 64-bit offset in a stack buffer and then copies 19 bytes (8 bytes offset, 11 bytes unitialized) behind the e9 opcode into the target function. By pure chance the jump still works, because amd64 is a little endian architecture, so the high extra 4 bytes offset are simply ignored."
The Linux rootkit does not appear to be a modified version of any known piece of malware and it first came to light last week when someone posted a quick description and analysis of it on the Full Disclosure mailing list. That poster said that his site had been targeted by the malware and some of his customers had been redirected to malicious sites.
The rootkit, like many pieces of malware, relies on a remote command-and-control server for some instructions. The server is still active right now and researchers said that it has some other related tools stored on it, as well.
In order to inject the iframes onto targeted sites the rootkit uses a custom method.https://threatpost.com/en_us/blogs/new-linux-rootkit-emerges-112012