Vulnerability Discussion

The ability to log in to another user's active or locked session must be disabled.

WARNING: This rule may cause issues when platformSSO is configured.

macOS has a privilege that can be granted to any user that will allow that user to unlock active users' sessions. Disabling the administrator's and/or user's ability to log in to another user's active and locked session prevents unauthorized people from viewing potentially sensitive and/or personal information.

Note: Configuring this setting will change the user experience and disable TouchID from unlocking the screen saver. To restore the user experience and allow TouchID to unlock the screen saver, run "/usr/bin/sudo /usr/bin/defaults write /Library/Preferences/com.apple.loginwindow screenUnlockMode -int 1". This setting can also be deployed with a configuration profile.

Satisfies: SRG-OS-000104-GPOS-00051, SRG-OS-000109-GPOS-00056

Check

Verify the macOS system is configured to disable login to other users' active and locked sessions with the following command:

RESULT="FAIL"
SS_RULE=$(/usr/bin/security -q authorizationdb read system.login.screensaver 2>&1 | /usr/bin/xmllint --xpath "//dict/key[.='rule']/following-sibling::array[1]/string/text()" -)

if [[ "${SS_RULE}" == "authenticate-session-owner" ]]; then
RESULT="PASS"
else
PSSO_CHECK=$(/usr/bin/security -q authorizationdb read "$SS_RULE" 2>&1 | /usr/bin/xmllint --xpath '//key[.="rule"]/following-sibling::array[1]/string/text()' -)
if /usr/bin/grep -Fxq "authenticate-session-owner" <<<"$PSSO_CHECK"; then
RESULT="PASS"
fi
fi

echo $RESULT

If the result is not "PASS", this is a finding.

Fix

Configure the macOS system to disable login to other users' active and locked sessions with the following command:

SS_RULE=$(/usr/bin/security -q authorizationdb read system.login.screensaver 2>&1 | /usr/bin/xmllint --xpath "//dict/key[.='rule']/following-sibling::array[1]/string/text()" -)

if [[ "$SS_RULE" == *psso* ]]; then
/usr/bin/security -q authorizationdb read psso-screensaver > "/tmp/psso-screensaver-mscp.plist"
/usr/bin/sed -i.bak 's/<string>authenticate-session-owner-or-admin<\/string>/<string>authenticate-session-owner<\/string>/' /tmp/psso-screensaver-mscp.plist
/usr/bin/security -q authorizationdb write psso-screensaver-mscp < /tmp/psso-screensaver-mscp.plist
/usr/bin/security -q authorizationdb write system.login.screensaver psso-screensaver-mscp 2>&1
else
/usr/bin/security -q authorizationdb write system.login.screensaver "authenticate-session-owner" 2>&1
fi