Two days ago I set up a new virtual machine for applications that require isolated security. When I put my computer into Connected Standby mode, I noticed SoC fan didn’t stop. To verify whether it was OS inconsistency or persistent issue, I manually initiated a system restart. However, it froze at login screen then. Nothing responded, including Ctrl + Alt + Delete key sequence. Attempting to force shutdown and start the computer almost didn’t improve the situation. After about ten attempts I managed to enter my desktop. There was no clue in event viewer: everything went well then suddenly the system froze.
I remembered that an alternative OS loader entry was configured to bypass Hypervisor launch at startup. I selected this entry to see whether it was related to Hyper-V. Test results indicated the freeze issue was strongly related to Hyper-V.
I tried to remember what I did before virtual machine configuration. I removed a virtual switch bridged to Surface Ethernet Adapter on my Surface Dock, then added a virtual switch bridged to VMware NAT adapter (which works better with Wireless network). Then I checked adapters in Network and Sharing Center, the old virtual switch didn’t get removed at all – and the “Remove” menu entry was unavailable. At last, I removed this adapter from Device Manager, and the issue was resolved.
This issue is likely related to OS inconsistency. When Hyper-V infrastructure attempts to initialize (bring up) all enabled network adapters including these Hyper-V virtual switches, the “removed” adapter is brought up, then enters failure state due to inconsistency in configuration. Because host operating system is a virtual machine on Hyper-V (with privileges), the host OS didn’t even get a chance to record what happened at that point.
The good thing is that I fixed it by myself; The bad thing is I missed an opportunity to report this bug and let Microsoft fix it.
When Microsoft decided to adopt MSBuild on .NET Core platform, project.json was not dropped immediately until first toolchain RTM arrives. Dotnet Development on Universal Windows Platform Development leverages .NET Core too, but the depreciation progress is significantly slower than other .NET Core platforms due to historical reasons. UWP uses project.json for package management and MSBuild for builds.
In Visual Studio 2017 April Update, Microsoft finally migrates new UWP projects to full MSBuild-based project system. But our projects, which creates on early 2015, doesn’t get an auto migration as expected. Hence we decided to migrate them manually for additional benefits like better toolchain stability and advanced customization features.
Reminder: Do not attempt to use “dotnet migrate” CLI command, it won’t work for UWP projects.
Notify all your team members. Make sure everyone has Visual Studio 2017 with April update installed.
If you have continuous integration environment configured, make sure build agents have NuGet 4.1 or higher installed (3.5 or 4.0 won’t work).
Lock VCS during migration to prevent additional incidents. (We’re using TFVC for source management so that it will be easy)
Clean up all projects (including bin and obj directories)
Iterate all project directories
Find C# project file, open with your favorite editor.
Add following property group before project file lists:
First of all, Windows “Gatekeeper” doesn’t block the execution of applications that don’t require installation. I tried to run PuTTY, a popular tool on Windows and it works.
Secondly, Windows “Gatekeeper” is based on Microsoft SmartScreen, which means disabling SmartScreen will turn it off too. Prior to application execution, SmartScreen will send file hash and publisher information(including certificate thumbprint) to Microsoft’s server, then SmartScreen server send back metadata including application reputation. Response is signed with a specific key that will be checked in client side for message integrity.
Unlike macOS, attempt to start application from console(e.g. Command Prompt and PowerShell) will trigger “Gatekeeper”.
The window is web-based. Although you can’t modify the response directly(no one wants to deal with sha256RSA unless the key leaks), you can attach a debugger to have some fun with it.
Microsoft claims that this feature is opt-in for most Windows SKUs (except Windows 10 Cloud AFAIK), and it is not revalent to UMCI (User-mode Code Integrity), which is enforced in Windows 10 Cloud.
Someone asked me if I could extract some images from a popular Chinese mobile game. I accepted the challenge, but things were far more complicated than I expected.
What I knew
This game is Unity3D-based.
Original assets were encrypted with known algorithm and key. DISCLAIMER: I will not tell you details about encryption.
The story began
I thought I could extract assets I needed with existing tools (e.g. Disunity) but I was proved wrong. Disunity has been refactored, and remaining work is still in progress (at least the moment I write this article). Since resource extraction has not been implemented at this moment, Disunity couldn’t be my choice.
Then I turned to a tool called Unity Assets Bundle Extractor. It did a great job extracting resources I needed graphically. However, acquiring thousands of texture assets from 2000+ isolated files is not an easy job. I tried the command line support but failed (maybe I was too stupid).
Luckily this toolkit provides some API and documentation. Since it was compiled with Microsoft Visual C++ 2010, I was unable to use it directly(C++ ABI constantly changes with every MSVC release). And I was too lazy to write a C wrapper for P/Invoke. But these C++ header files point to a perfect solution – parse file and implement my own UnityFS parser/reader.
Special thank to the UABE project – without these generous header, I would not be able to implement my own parsing and compose this article.
UnityFS was a new asset bundle format introduced in Unity 5. I am not a Unity3D developer, and I absolutely didn’t know why Unity introduce a new bundle format. But anyway, let’s analyze it.
Things you need to know
UnityFS is just bundle of several Unity assets. Each asset contains a collection of serialized Unity objects (e.g. 2D texture, text resources, scene objects, etc.).
UnityFS follows a standard Unity file header structure. Let’s call it AssetsBundleHeader06
You have to parse asset files in order to extract what you need. There’s bunch of documentation about this. Look into the old Disunity source code for some idea.
So the header goes like this. There’s a DWORD flags data that matters – it contains some critical information required for decompression and directory parsing. The rule goes like this:
(Flags & 0x3F) is compression mode. 0 means no compression, 1 means LZMA and 2/3 means LZ4/LZ4HC.
(Flags & 0x40) says whether the bundle has directory info.
(Flags & 0x80) says whether the block and directory list is at the end of this bundle file.
C# provides a good BinaryReader that makes things a bit easy. But it can be improved for better Null-terminated String and Big Endian support. Be careful with endianness. Unity utilizes both Big Endian and Little Endian in a single file and personally I didn’t get this. For the sake of convenience, I extended the original BinaryReader for these support. Length of each data type matters – but that’s a basic stuff for CS students.
UnityFS uses optional block-based compression for streaming (you can read a specific bundle without downloading the whole file). Both LZMA and LZ4* (LZ4Hc, etc.) are supported. The Unity’s proprietary parser and Disunity respects this design. But I just wanted these bundle files, so I decided to read all blocks at once and decompress into a single memory stream.
You can implement your own block-based reader – but my time budget didn’t allow me to do this.
There we go…block and file information!
Following a unknown 16 bytes block, there’s a Big-Endian UInt32 value represents block count in a single package. Each block information contains a Big-Endian UInt32 decompressed size, a Big-Endian UInt32 compressed size and a flag that we might not interested in.
Then a BE UInt32 value represents file count in a single package. Each file information contains file offset we need(BE UInt64), the decompressed size(BE UInt64), a BE UInt32 flag and a Null-Terminated string of file name.
Parse your assets now
With sufficient information we retrieved, we were able to extract raw asset files from a UnityFS bundle. Then what you need is search the Internet for ideas of extracting objects(text resources, 2D texture, etc.) from Unity assets. Good luck on exploring!
In this article, we discussed structure and parsing of UnityFS resource bundle file. For more information about UnityFS and Unity asset files, please research these projects I mentioned in this article.
Previously my openconnect server deployment plan utilizes PAM authentication (via Kerberos/Active Directory) as the primary authentication method. It works but it’s complicated (password every time). I just enabled certificate authentication today and it worked fine.
Things to note
Enable certificate authentication as an alternative authentication method (up to you, but some guys in our domain don’t use certificate-capable device)
Use “Smartcard Logon” certificate template with subject information in “Common Name” style
Set OID 184.108.40.206 as user identifier in openconnect server configuration
Provision root CA, CRL and OCSP (CRL and OCSP are optional but essential as part of the best-practice)
I provisioned the same certificate in my Yubikey PIV and TPM-based virtual smartcard, but neither works for AnyConnect client. Certificate in user certificate store is fine.