OSX/Proton spreading again through supply‑chain attack

On 19 October 2017, ESET researchers noticed that Eltima, the makers of the Elmedia Player software, were distributing a version of their application trojanized with the OSX/Proton malware on their official website. ESET contacted Eltima as soon as the situation was confirmed. Eltima was very responsive and maintained an excellent communication with us throughout the incident.

Timeline

• 2017-10-19 : Trojanized package confirmed
• 2017-10-19 10:35am EDT: Eltima informed via email
• 2017-10-19 2:25pm EDT: Eltima acknowledged the issue and initiated remediation efforts
• 2017-10-19 3:10pm EDT: Eltima confirms their infrastructure is cleaned up and serving the legitimate applications again
• 2017-10-19 10:12am EDT: Eltima publishes an announcement about the event
• 2017-10-20 12:15pm EDT: Added references to Folx that was also distributed with the Proton malware

Note: This blog was initially posted despite our research being incomplete. Hence, this information is preliminary and the blogpost will be updated as new facts emerge.

Am I compromised?

ESET advises anyone who downloaded Elmedia Player or Folx software recently to verify if their system is compromised by testing the presence of any of the following files or directories:

• /tmp/Updater.app/
• /Library/LaunchAgents/com.Eltima.UpdaterAgent.plist
• /Library/.rand/
• /Library/.rand/updateragent.app/

If any of them exists, it means the trojanized Elmedia Player or Folx application was executed and that OSX/Proton is most likely running.

If you have downloaded that software on October 19th before 3:15pm EDT and run it, you are likely compromised.

As far as we know, the trojanized version of the application was only downloadable from the Eltima website, between 08:00 and 15:15 EDT on 19 October 2017. The built-in automatic update mechanism seems unaffected.

What does the malicious payload do to a compromised system?

OSX/Proton is a backdoor with extensive data-stealing capabilities. It gains persistence on the system and can steal the following:

• Operating system details: hardware serial number (IOPlatformSerialNumber), full name of the current user, hostname, System Integrity Protection status (csrutil status), gateway information (route -n get default | awk ‘/gateway/ { print $2 }’), current time & timezone
• Browser information from Chrome, Safari, Opera and Firefox: history, cookies, bookmarks, login data, etc.
• Cryptocurrency wallets:
  • Electrum: ~/.electrum/wallets
  • Bitcoin Core: ~/Library/Application Support/Bitcoin/wallet.dat
  • Armory: ~/Library/Application Support/Armory
• SSH private data (entire .ssh content)
• macOS keychain data using a modified version of chainbreaker
• Tunnelblick VPN configuration (~/Library/Application Support/Tunnelblick/Configurations)
• GnuPG data (~/.gnupg)
• 1Password data (~/Library/Application Support/1Password 4 and ~/Library/Application Support/1Password 3.9)
• List of all installed applications.

How do I clean my system?

As with any compromise of an administrator account, a full OS reinstall is the only sure way to get rid of the malware. Victims should also assume at least all the secrets outlined in the previous section are compromised and take appropriate measures to invalidate them.

Supply-chain attack revisited on the Mac

Last year, the Mac Bittorrent client Transmission was abused twice to spread malware, first the OSX/KeRanger ransomware followed by OSX/Keydnap password stealer. Then this year, the Handbrake video-transcoder application was found bundled with OSX/Proton.

Today, ESET discovered another popular Mac software package being used to spread OSX/Proton: Elmedia Player, a media player that reached the 1,000,000 users milestone this summer:

Technical analysis

OSX/Proton is a RAT (Remote Access Trojan) sold as a kit on underground forums. It was very briefly documented by Sixgill earlier this year and then further analyzed by Thomas Reed at MalwareBytes, Amit Serper at CyberReason and Patrick Wardle at Objective-See.

In the current case of Eltima trojanized software, the attacker built a signed wrapper around the legitimate Elmedia Player and Proton. In fact, we observed what seems to be real-time repackaging and signing of the wrappers, all with the same valid Apple Developer ID. See the history of currently known samples below. Eltima and ESET confirmed they are working with Apple to invalidate the Developer ID used to sign the malicious application. (Apple revoked the certificate.)

(timestamps are all in EDT timezone)

Clean application:

Timestamp	Developper ID	SHA-1
Timestamp=Jul 24, 2017, 4:56:24 AM	Authority=Developer ID Application: ELTIMA LLC (N7U4HGP254)	0603353852e174fc0337642e3957c7423f182a8c

Trojanized application:

Timestamp	Developper ID	SHA-1 (dmg file)
Timestamp=Oct 19, 2017, 8:00:05 AM	Authority=Developer ID Application: Clifton Grimm (9H35WM5TA5)	e9dcdae1406ab1132dc9d507fd63503e5c4d41d9
Timestamp=Oct 19, 2017, 12:22:24 PM	Authority=Developer ID Application: Clifton Grimm (9H35WM5TA5)	8cfa551d15320f0157ece3bdf30b1c62765a93a5
Timestamp=Oct 19, 2017, 2:00:38 PM	Authority=Developer ID Application: Clifton Grimm (9H35WM5TA5)	0400b35d703d872adc64aa7ef914a260903998ca

First, the wrapper launches the real Elmedia Player application stored in the Resources folder of the application:

And finally extracts & launches OSX/Proton:

As seen in previous cases, OSX/Proton shows a fake Authorization window to gain root privileges:

Persistance

OSX/Proton ensures persistence by adding a LaunchAgent for all users when the administrator types their password. It creates the following files on the system:

• /Library/LaunchAgents/com.Eltima.UpdaterAgent.plist
• /Library/.rand/updateragent.app

Backdoor commands

As mentioned at the beginning of the post, OSX/Proton is a backdoor with extensive information stealing capabilities. The backdoor component we observed supports the following commands:

archive	Archive files using zip
copy	Copy file locally
create	Create directory or file locally
delete	Delete file locally
download	Download file from a URL
file_search	Search for files (executes find / -iname \"%@\" 2> /dev/null)
force_update	Self-update with digital signature validation
phonehome
remote_execute	Execute the binary file inside a .zip file or a given shell command
tunnel	Create SSH tunnel using port 22 or 5900
upload	Upload file to C&C server

C&C server

Proton uses a C&C domain that mimics the legitimate Eltima domain, which is consistent with the Handbrake case:

	Legitimate domain	Proton C2 domain
Eltima	eltima.com	eltima[.]in
Handbrake	handbrake.fr	handbrakestore[.]com
		handbrake[.]cc

IOCs

URL distributing the trojanized application at the time of discovery:

• hxxps://mac[.]eltima[.]com/download/elmediaplayer.dmg
• hxxp://www.elmedia-video-player.[.]com/download/elmediaplayer.dmg
• hxxps://mac.eltima[.]com/download/downloader_mac.dmg

C&C servers

eltima[.]in / 5.196.42.123 (domain registered 2017-10-15)

Hashes

Path	SHA-1	ESET Detection name	Description
Elmedia Player.app/Contents/Resources/.pl.zip	9E5378165BB20E9A7F74A7FCC73B528F7B231A75	multiple threats	ZIP archive with the Proton malware and Python scripts
	10A09C09FD5DD76202E308718A357ABC7DE291B5	multiple threats	ZIP archive with the Proton malware and Python scripts
Elmedia Player.app/Contents/MacOS/Elmedia Player	C9472D791C076A10DCE5FF0D3AB6E7706524B741	OSX/Proton.D	Launcher (or wrapper)
	30D77908AC9D37C4C14D32EA3E0B8DF4C7E75464	OSX/Proton.D	Launcher (or wrapper)
Updater.app/Contents/MacOS/Updater	3EF34E2581937BABD2B7CE63AB1D92CD9440181A	OSX/Proton.C	Proton malware, not signed
	EF5A11A1BB5B2423554309688AA7947F4AFA5388	OSX/Proton.C	Proton malware, not signed

Hat tip to Michal Malik, Anton Cherepanov, Marc-Étienne M. Léveillé, Thomas Dupuy & Alexis Dorais-Joncas for their work on this investigation.