Discovered: September 30, 2011
Updated: April 06, 2012 3:47:44 PM
Systems Affected: Mac
OSX.Flashback is a Trojan horse that gathers information from the compromised computer.
Antivirus Protection Dates
- Initial Rapid Release version September 30, 2011 revision 018
- Latest Rapid Release version January 15, 2018 revision 020
- Initial Daily Certified version September 30, 2011 revision 021
- Latest Daily Certified version January 15, 2018 revision 024
- Initial Weekly Certified release date October 05, 2011
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.
The Trojan may arrive as the following PKG file:
When executed, the Trojan may create one of the following sets of files:
- /Applications/Safari.app/Contents/Resources/.[THREAT FILE NAME].png
- [CURRENT USER HOME FOLDER]/Library/Application Support/.[THREAT FILE NAME].tmp
- [CURRENT USER HOME FOLDER]/.MacOSX
It then 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:
- Kernel information
- Machine type
- OS information
- User ID
The Trojan deletes itself if any of the following applications are present on the computer:
- /Library/Little Snitch
- /Applications/VirusBarrier X6.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 Trojan may then modify one of the following files:
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:
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.
The following instructions pertain to all current and recent Symantec antivirus products for Macintosh.
- Update the virus definitions.
- Run a full system scan and repair or delete all the files detected.
1. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
- Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
- Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response website and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
2. To scan for and delete the infected files
- Start your Norton AntiVirus or Symantec Endpoint Protection for Macintosh program and make sure that it is configured to scan all files.
- Run a full system scan.
- If any files are detected, click Repair (if available) or Delete.
Writeup By: Kevin Savage, Karthik Selvaraj and Branko Spasojevic