Cisco AnyConnect Path Traversal / Privilege Escalation

The installer component of Cisco AnyConnect Secure Mobility Client for Windows prior to version 4.8.02042 is vulnerable to path traversal and allows local attackers to create/overwrite files in arbitrary locations with system level privileges. The attack consists in sending a specially crafted IPC request to the TCP port 62522 on the loopback device, which is exposed by the Cisco AnyConnect Secure Mobility Agent service. This service will then launch the vulnerable installer component (vpndownloader), which copies itself to an arbitrary location before being executed with system privileges. Since vpndownloader is also vulnerable to DLL hijacking, a specially crafted DLL (dbghelp.dll) is created at the same location vpndownloader will be copied to get code execution with system privileges. This exploit has been successfully tested against Cisco AnyConnect Secure Mobility Client versions 4.5.04029, 4.5.05030 and 4.7.04056 on Windows 10 version 1909 (x64) and Windows 7 SP1 (x86).