- 1.安装Google Chrome 32bit版本(32版本容易使用工具进行调试)
- 2.Chrome内置的CDM是Widevine(几年前收购来的),目录在Google\Chrome\Application\58.0.3029.110\WidevineCdm,在子目录_platform_specific\win_x86有下2个dll:
- widevinecdm.dll - widevine核心模块,导出的函数有:InitializeCdmModule_4,DeinitializeCdmModule,CreateCdmInstance,GetCdmVersion,GetHandleVerifier
- widevinecdmadapter.dll - PPAPI插件标准适配库,导出函数有:PPP_GetInterface,PPP_InitializeModule,PPP_ShutdownModule
- 3.正常情况下播放DRM视频的流程:
- Chrome -> Widevine CDM Adapter(widevinecdmadapter.dll) -> Widevine CDM Module (widevinecdm.dll)
- widevinecdmadapter.dll调用widevinecdm.dll的导出函数CreateCdmInstance来创建CDM实例.
- 4.CDM框架是Google Chrome的标准,所以API参数和接口都有C++ include文件,比如API CreateCdmInstance:
- CDM_API void* CreateCdmInstance(int cdm_interface_version, const char* key_system, uint32_t key_system_size, GetCdmHostFunc get_cdm_host_func, void* user_data);
-
- CDM实例要继承于class ContentDecryptionModule_8,查看class ContentDecryptionModule_8,发现了一个非常重要的函数:Decrypt,主要是将加密的数据传入,解密后的数据传出,我的天呐,只要截获了这个函数不就搞定了吗!!!
- class CDM_CLASS_API ContentDecryptionModule_8 {
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- virtual Status Decrypt(const InputBuffer& encrypted_buffer,
- DecryptedBlock* decrypted_buffer) = 0;
- };
5.了解了API参数和class定义后,就设想如果在widevinecdmadapter.dll 和 widevinecdm.dll之间在互相调用时截获到解密后的数据就可以绕过DRM保护机制.
6.开始写一个DLL, 名为CdmProxy.dll, 我自己的CreateCdmInstance函数,这部分不解释了:
- extern "C" __declspec(dllexport) void * CDMAPI_DEFINE my_CreateCdmInstance(int cdm_interface_version, const char* key_system,
- uint32_t key_system_size, GetCdmHostFunc get_cdm_host_func, void* user_data)
- {
- gHostUserData = user_data;
- wsprintf(wchLog, L"CdmProxy - call CreateCdmInstance(%d, %S, %d, 0x%08X, 0x%08X)",
- cdm_interface_version, key_system, key_system_size, get_cdm_host_func, user_data);
- OutputDebugStringW(wchLog);
- void *p = pCreateCdmInstance(cdm_interface_version, key_system, key_system_size, get_cdm_host_func, user_data);
-
- cdm::ContentDecryptionModule_8 *pCdmModule = (cdm::ContentDecryptionModule_8 *)(p);
- MyContentDecryptionModuleProxy *pMyCdmModule = new MyContentDecryptionModuleProxy(pCdmModule);
-
- return pMyCdmModule;
- }
我的代{过}{滤}理class MyContentDecryptionModuleProxy,代码不解释:
// class MyContentDecryptionModuleProxy
- class MyContentDecryptionModuleProxy : public cdm::ContentDecryptionModule_8
- {
- public:
- MyContentDecryptionModuleProxy(cdm::ContentDecryptionModule_8 *pCdm)
- {
- mCdm = pCdm;
- }
- private:
- cdm::ContentDecryptionModule_8 *mCdm;
-
- public:
-
- virtual cdm::Status Decrypt(const cdm::InputBuffer& encrypted_buffer, cdm::DecryptedBlock* decrypted_buffer)
- {
- cdm::Status status = cdm::kSuccess;
- codelive();
- DebugDecryptBreak(encrypted_buffer.iv, encrypted_buffer.key_id, encrypted_buffer.data);
- status = mCdm->Decrypt(encrypted_buffer, decrypted_buffer);
-
- string strIV = data2HexString((const char *)encrypted_buffer.iv, encrypted_buffer.iv_size);
- string strEncData = data2HexString((const char *)encrypted_buffer.data, min(encrypted_buffer.data_size, 32));
- string strDecData = data2HexString((const char *)decrypted_buffer->DecryptedBuffer()->Data(),
- min(decrypted_buffer->DecryptedBuffer()->Size(), 32));
- wsprintf(wchLog, L"CdmProxy - call Decrypt(IV:%S, encData(%d):%S, decData(%d):%S)",
- strIV.c_str(), encrypted_buffer.data_size, strEncData.c_str(),
- decrypted_buffer->DecryptedBuffer()->Size(), strDecData.c_str());
- OutputDebugStringW(wchLog);
-
- if(mEncFile == NULL)
- {
- mEncFile = fopen("d:\\cdm_enc.bin", "wb");
- }
- if(mEncFile != NULL)
- {
- fwrite(encrypted_buffer.data, 1, encrypted_buffer.data_size, mEncFile);
- }
- if(mDecFile == NULL)
- {
- mDecFile = fopen("d:\\cdm_dec.bin", "wb");
- }
- if(mDecFile != NULL)
- {
- fwrite(decrypted_buffer->DecryptedBuffer()->Data(), 1, decrypted_buffer->DecryptedBuffer()->Size(), mDecFile);
- }
- return status;
- }
- };
7.核心代码写完了,就要解决DLL加载的问题,尝试了几种简单的方式,分别把widevinecdm.dll和widevinecdmadapter.dll改名为widevinecdm_org.dll和widevinecdmadapter_org.dll,然后自己写一个DLL,导出和widevinecdm.dll或者widevinecdmadapter.dll相同的API,然后再调用原来DLL的方式,但这种方式发现不可行,原因在于Chrome的安全沙盒,所有的插件都是加载的沙盒进程空间,敏感的API都无法使用,比如:ReadProcessMemory,CeateFile,OutputDebugString等等. 逃脱沙盒(Sandbox Escape)是Google奖金数额非常高的,最高可达$15,000.
8.既然进程都是Chrome创建的,所以就直接对chrome.exe下手,直接patch chrome.exe,让其加载我的CdmProxy.dll,结果成功了,毕竟chrome启动时还未启用沙盒机制,所以没花费太多技术就解决了DLL加载问题.
9.改变API截获方式,对widevinecdmadapter.dll进行动态的补丁,将调用API CreateCdmInstance的地址改为我自己的API my_CreateCdmInstance,然后在DLL加载时进行以下处理:
- BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved)
- {
- switch(ul_reason_for_call)
- {
- case DLL_PROCESS_ATTACH:
- {
- hWideVineCdm = LoadLibraryW(L"{PATH}\\widevinecdm.dll");
-
- pInitializeCdmModule_4 = (InitializeCdmModule_4Func)GetProcAddress(hWideVineCdm, "InitializeCdmModule_4");
- pDeinitializeCdmModule = (DeinitializeCdmModuleFunc)GetProcAddress(hWideVineCdm, "DeinitializeCdmModule");
- pCreateCdmInstance = (CreateCdmInstanceFunc)GetProcAddress(hWideVineCdm, "CreateCdmInstance");
- pGetCdmVersion = (GetCdmVersionFunc)GetProcAddress(hWideVineCdm, "GetCdmVersion");
-
- hWideVineCdmAdapter = LoadLibraryW(L"{PATH}\\widevinecdmadapter.dll");
- if(hWideVineCdmAdapter != NULL)
- {
- DWORD dwSrcAddr = (DWORD)hWideVineCdmAdapter + 0x0000446D;
- const BYTE chVerify[] = { 0xFF, 0x15 };
- BOOL isOK = patch_DsCallFunction(dwSrcAddr, (DWORD)my_CreateCdmInstance, chVerify, sizeof(chVerify));
- wsprintf(wchLog, L"CdmProxy - patch CreateCdmInstance, Address:0x%08X-0x%08X, %s.",
- dwSrcAddr, (uint32_t)my_CreateCdmInstance,
- isOK ? L"OK" : L"FAILED");
- OutputDebugStringW(wchLog);
- }
- }
- break ;
- }
- }
10.然后进行测试,播放一个有DRM保护的DASH视频:
https://shaka-player-demo.appspo ... gleKey/Manifest.mpd
发现文件没保存下来,LOG也没输出,想必是安全沙盒起作用了。
11.又要逃脱沙盒,经过研究,发现根本不需要,只要在chrome启动参数增加 --no-sandbox 即可。我的天呐,为啥要提供这样一个后门啊!!!
12.再次播放加密的视频,文件顺利保存下来,LOG也输出成功,经验证,解密后的数据与之前未加密的数据是一致的。
13.Google Chrome的CDM就这样被破解了,非常的简单的就绕过了Widevine DRM的算法,这应该是Chrome CDM的框架设计的严重问题,估计要改变也不是非常容易的。
这是LOG数据:
- ( "CdmProxy - call CreateCdmInstance(8, com.widevine.alpha, 18, 0x70F86310, 0x00D75A88)" ) 0.0001399
- ( "CdmProxy - call CreateCdmInstance(8, com.widevine.alpha, 18, 0x70F86310, 0x00D757C8)" ) 0.0000937
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F00000000000000000, encData(348):FFF158402B9FFC2FF05300F2BF83E9A0, decData(0):)" ) 0.0001350
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F00000000000000000, encData(348):FFF158402B9FFC2FF05300F2BF83E9A0, decData(348):FFF158402B9FFC00D03403E95B8639BD)" ) 0.0001335
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F00000000000000000, encData(348):FFF158402B9FFC2FF05300F2BF83E9A0, decData(348):FFF158402B9FFC00D03403E95B8639BD)" ) 0.0001032
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F10000000000000000, encData(348):FFF158402B9FFC487380B8930FFFAB41, decData(348):FFF158402B9FFC00F43420C24620902C)" ) 0.0001392
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F20000000000000000, encData(349):FFF158402BBFFC1175E15FE4B6154B30, decData(349):FFF158402BBFFC00FA342D90762A3188)" ) 0.0001032
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F30000000000000000, encData(348):FFF158402B9FFCC45D5715E87235E5CF, decData(348):FFF158402B9FFC00F8342CEC825A2D85)" ) 0.0000994
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F40000000000000000, encData(348):FFF158402B9FFC6749FBAF64926471DE, decData(348):FFF158402B9FFC00F83421884529290A)" ) 0.0000880
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F50000000000000000, encData(349):FFF158402BBFFCF8132EFC31C186DDE1, decData(349):FFF158402BBFFC00F2342D9049124988)" ) 0.0001088
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F60000000000000000, encData(348):FFF158402B9FFC82EDA0BD4AB7158938, decData(348):FFF158402B9FFC00EE342D7475223D85)" ) 0.0001035
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F70000000000000000, encData(348):FFF158402B9FFC4B2C585CC10F74036E, decData(348):FFF158402B9FFC00F4342D74662A2088)" ) 0.0001555
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F80000000000000000, encData(349):FFF158402BBFFCCF33665AC4E219EC92, decData(349):FFF158402BBFFC00FA342E30547B0604)" ) 0.0001494
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818F90000000000000000, encData(348):FFF158402B9FFC2C9A7362594261CE23, decData(348):FFF158402B9FFC00F4342E305429150A)" ) 0.0004035
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818FA0000000000000000, encData(348):FFF158402B9FFC1905A086AE3CEF0AEC, decData(348):FFF158402B9FFC00EE342E3456391906)" ) 0.0005913
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818FB0000000000000000, encData(349):FFF158402BBFFC8D0EB865013262FB6E, decData(349):FFF158402BBFFC00F6342E34563A2186)" ) 0.0001479
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818FC0000000000000000, encData(348):FFF158402B9FFC484211C612F22283FB, decData(348):FFF158402B9FFC0102342E74482A2E02)" ) 0.0002507
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818FD0000000000000000, encData(348):FFF158402B9FFC283122B1DDE740DAC2, decData(348):FFF158402B9FFC0104342EB464190D08)" ) 0.0003011
- ( "CdmProxy - call Decrypt(IV:6CD1F4FBCE5818FE0000000000000000, encData(349):FFF158402BBFFCAC8759D48FF1A258A3, decData(349):FFF158402BBFFC010E342ED04A1A2982)" ) 0.0003095
DRM这么多年了,很多保护机制和算法都做的非常严密,但还是被Zhu一样的队友给出卖了。
公开这个研究,是为了让广大的视频公司不要以为DRM非常的安全,有时候真的是不堪一击,某个环节出现漏洞,同样面临极大的安全问题。
我提交后,Chromium团队很快的做出了回复,他们确认这是一个重大的安全问题,而且影响所有运行Chrome浏览器的操作系统,包括: Linux, Windows, Chrome, Mac等等. 但另一个员工说这是一个已知的问题,并提供了一个issue号: 658022,但我无限查看漏洞内容是否与我提交的一致。之后我向google 团队的几个成员发了邮件,说既然是已知的问题,那也就是不符合奖励规则,因此我也就可以公布细节,让视频内容公司重视这个问题,以便尽早的商讨更加安全的解决方案。如果此篇文章不适合公布,请通知我,谢谢。
没看懂是什么。