ELF_CDORKED.A

 Analysis by: Rhena Inocencio

 ALIASES:

Linux/Cdorked.A trojan (NOD32), Linux/Cdorked-A (Sophos)

 PLATFORM:

Linux

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware


This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size:

Varies

File Type:

ELF

Memory Resident:

Yes

Initial Samples Received Date:

27 Apr 2013

Payload:

Connects to URLs/IPs, Compromises system security

Arrival Details

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Update URLs for redirection
  • Update whitelisted and blacklisted User-Agents
  • Update blacklisted IP range list
  • Update whitelisted IP range list
  • Update list of blacklisted pages
  • Update list of whitelisted pages
  • Update list of excluded Accept-Language
  • Show server status

NOTES:

It redirects users to websites with the following format:

  • http://{16 random characters}.{domain name}/index.php?{letter}={encoded base64 string}

The following strings are used to check the server name:

  • adm
  • bill
  • bucks
  • cpanel
  • host
  • memb
  • mrtg
  • secur
  • stat
  • submit
  • support
  • webmaster
  • webmin

The commands are sent to the infected server via HTTP request through a specially crafted URL.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.908.08

FIRST VSAPI PATTERN DATE:

10 May 2013

VSAPI OPR PATTERN File:

9.909.00

VSAPI OPR PATTERN Date:

10 May 2013

Scan your computer with your Trend Micro product to delete files detected as ELF_CDORKED.A. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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