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MAC OSX Flashback Backdoor Trojan (Sep 29, 2011)

by Security News

SonicWALL UTM Research team received reports of a new MAC OSX Flashback Trojan spreading in the wild by masquerading as a Adobe flash player 11 installer. Once installed it proceeds to install a backdoor on the system, contacts a remote server to report infection and awaits further instructions.

The fake installer is automatically executed when downloaded through Safari. The user is then led through the following installation screens:

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It performs the following activities when installed:

  • It drops the following files:
    • ~/Library/Preferences/Preferences.dylib
    • ~/.MacOSX/environment.plist
    • /tmp/AdobeUpdate/FlashPlayer.txt
  • The preinstall script removes the downloaded "FlashPlayer-11-macos.pkg" file once installation is completed.
  • It checks for presence of "Little Snitch" security software by querying for "/Library/Little Snitch/lsd" and disables it.
  • It modifies the "DYLD_INSERT_LIBRARIES" environment variable for "launchd" to point to "~/Library/Preferences/Preferences.dylib". This ensures malicious Preferences.dylib is loaded when certain applications/daemons are launched.
  • It reports infection to remote server. 
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  • The user agent used when reporting to the remote server is combination of kernel variables "hw.machine" and "kern.osrelease" read from the infected system.

We advice users to only download software from trusted sources. We also recommend disabling "Open safe files after downloading" feature in Safari which will prevent this Trojan installer from automatically launching on download. This feature can be unchecked in Safari->Preferences->General: 

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SonicWALL Gateway AntiVirus provides protection against this threat with the following signature:

  • GAV: GAV: OSX.Flashback.A (Trojan)

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    The SonicWall Capture Labs Threat Research Team gathers, analyzes and vets cross-vector threat information from the SonicWall Capture Threat network, consisting of global devices and resources, including more than 1 million security sensors in nearly 200 countries and territories. The research team identifies, analyzes, and mitigates critical vulnerabilities and malware daily through in-depth research, which drives protection for all SonicWall customers. In addition to safeguarding networks globally, the research team supports the larger threat intelligence community by releasing weekly deep technical analyses of the most critical threats to small businesses, providing critical knowledge that defenders need to protect their networks.