1. Symantec/
  2. Security Response/
  3. OSX.Flashback.K


Risk Level 2: Low

April 9, 2012
April 13, 2012 10:49:02 AM
Also Known As:
Trojan-Downloader.OSX.Flashfake.ab [Kaspersky]
Infection Length:
Systems Affected:
CVE References:
This Trojan may arrive on the compromised computer by exploiting the Oracle Java SE Remote Java Runtime Environment Denial Of Service Vulnerability (BID 52161).

When executed, the Trojan creates a semaphore with the following name:

Next, it attempts to run the following file using the system() command:

The Trojan then obtains the following system information from the compromised computer:
  • HW.machine
  • Kernel information
  • Machine type
  • OS information
  • Password
  • User ID

The Trojan deletes itself if any of the following applications are present on the computer:
  • /Library/Little Snitch
  • /Developer/Applications/Xcode.app/Contents/MacOS/Xcode
  • /Applications/VirusBarrier X6.app
  • /Applications/iAntiVirus/iAntiVirus.app
  • /Applications/avast!.app
  • /Applications/ClamXav.app
  • /Applications/HTTPScoop.app
  • /Applications/Packet Peeper.app

If none of the above applications are present, the Trojan connects to the following location and downloads more files on to the compromised computer:

The downloaded files are compressed and encrypted using RC4. It then decrypts and decompresses the files.

The Trojan may then modify one of the following files:
  • /Applications/Safari.app/Contents/Info.plist
  • ~/.MacOSX/environment.plist

It then sets the binary to the environment variable "DYLD_INSERT_LIBRARIES" using the command "launchctrl setenv DYLD_INSERT_LIBRARIES=" and exports it to ensure that it runs when the compromised computer starts.

Next, it connects to one of the following remote locations depending on successful installation:
  • [http://][REMOVED]
  • [http://][REMOVED]
  • [http://][REMOVED]


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Karthik Selvaraj
Summary| Technical Details| Removal

Search Threats

Search by name
Example: W32.Beagle.AG@mm
STAR Antimalware Protection Technologies
2016 Internet Security Threat Report, Volume 21
  • Twitter
  • Facebook
  • LinkedIn
  • Google+
  • YouTube