The revocation status of the domain controller certificate used for smartcard authentication could not be determined. There is additional information in the system event log. Please contact your system administrator.
If you have smartcard authentication set up for logging into certain Active Directory systems, and also a restrictive web proxy on the machine acting as the RDP client, you may run into this issue.
My mistake was checking that the RDP server had access to the CRL mentioned in the certificate.
Yes, the RDP server might be quite happy in terms of checking the certificate revocation, but if the RDP client can’t access the CRL URL (perhaps through the configured proxy), you will receive this same error.
Check connectivity to the stated CRL distribution point from the RDP client and RDP server!
I am intrigued by Trail of Bits’ new tool RPC Investigator. Exploring Windows internals is of ongoing interest, and this seems like a very interesting tool to shed light on some of that internal complexity and learn more about how the OS works.
Trail of Bits is releasing a new tool for exploring RPC clients and servers on Windows. RPC Investigator is a .NET application that builds on the NtApiDotNet platform for enumerating, decompiling/parsing and communicating with arbitrary RPC servers. We’ve added visualization and additional features that offer a new way to explore RPC.
RPC is an important communication mechanism in Windows, not only because of the flexibility and convenience it provides software developers but also because of the renowned attack surface its implementers afford to exploit developers. While there has been extensive research published related to RPC servers, interfaces, and protocols, we feel there’s always room for additional tooling to make it easier for security practitioners to explore and understand this prolific communication technology.
I could not find a binary release of the code on GitHub, just instructions on how to build it yourself.
Following teachers’ return for this academic year in September, we suddenly found ourselves with a frequent issue. After waking the Surface Pro devices from sleep, the Type Cover would often not respond to keystrokes. The on screen keyboard was not affected, but USB keyboards also stopped working. The Type Cover trackpad would continue working fine.
A full Windows restart would always bring back the keyboard functionality.
This triggered a challenging investigation to determine what was wrong. The fact that we had made no significant software changes that should affect this over the summer made me look, with guidance from Microsoft Surface Business support, to Windows Updates as a possible issue. Rolling back both September and August’s Windows Updates did not seem to have any effect.
Clearly this wasn’t a wide enough issue to be affecting everyone, or many more customers would be up in arms about having to restart 6 or 7 times in a working day!
With the issue affecting a wide range of different Surface Pro devices and different Type Covers, it looked more likely to be a software issue than hardware. Predictably, perhaps, I was unable to reproduce the issue on a device with nothing but a stock Windows install on it… it’s got to be software. Right?
The build of Windows we run is kept as simple and close-to-stock as possible, for exactly the reason that it saves you from this type of issue! Of the software we do run, the prime suspects seemed to be:
I dug a little deeper into what Veyon brings along to do its magic. Its ability to remotely control other systems for classroom management purposes, including remotely inducing the Secure Attention Sequence (Ctrl-Alt-Delete to normal folks!) means that it must have some kind of driver installed that permits this functionality. Eventually, it dawned on me that this interacts with the keyboard, making it a good candidate for the culprit for, you know, keyboard problems.
I ran into some trouble recently with a machine that had previously been registered for Intune/Microsoft Endpoint Manager AutoPilot deployment hanging on a Windows reinstall (the SSD had been replaced).
The machine would sit at “checking connection to Microsoft. This might take a while”.
Take a while it did — a spell overnight on this very screen would not help. I used Shift+F10 to get some diagnostics tooling on the system. I could see references to a /join HTTPS endpoint being accessed that seemed to be Intune-related, but it was neither obviously succeeding nor failing.
Some perusal of logfiles suggested to me that UEFI variables are involved in the AutoPilot process.
Fortunately, the machines in question are desktop PCs. A very simple way to (destructively!) clear out UEFI variables was to remove the CMOS battery for a period of time. Upon trying again, we jump right past “checking connection to Microsoft” and can move forward with the install.
On systems where a battery pull is not effective, it may be worth getting yourself into a UEFI shell and using dmpstore to identify UEFI variables in NVRAM that may be related to AutoPilot and deleting them. Sorry I can’t be more specific!
Today’s malware-loader-du-jour, Bumblebee, has been seen achieving initial access through phishing sites that convince a user to mount a downloaded ISO image. This may be a reaction to Microsoft’s recent improvements to macro-enabled document security.
Adversaries push ISO files through compromised email (reply) chains, known as thread hijacked emails, to deploy the Bumblebee loader. ISO files contain a byte-to-byte copy of low-level data stored on a disk. The malicious ISO files are delivered through Google Cloud links or password protected zip folders. The ISO files contain a hidden DLL with random names and an LNK file. DLL (Dynamic Link Library) is a library that contains codes and data which can be used by more than one program at a time. LNK is a filename extension in Microsoft Windows for shortcuts to local files.
One of the things that we can do to help our users avoid this new initial execution foothold is by blocking the mounting of ISO images, as long as you can be confident this will not break anything they actually need to do! I am fortunate enough to be able to do this.
Here is what I have rolled out as an Intune PowerShell Script to block the mounting of ISOs. No reboot is required. Users will see the Mount option disappear from the context menu of an ISO file within File Explorer and will be unable to double-click to mount a malicious ISO. Or, indeed, any ISO. 😉
We will head to Microsoft Endpoint Manager admin center, go to Devices > Scripts and create a new Windows 10 and later PowerShell script.
The Intune Script
UPDATE: I have made some improvements — namely, the previous one liner will cause failures to be reported in Intune on subsequent runs. We will now only add the value where it does not exist, and we will add support for Windows.VhdFile as well. It’s no longer a one-liner!
This doesn’t make you bulletproof, but will, if tolerated by your users, provide a substantial degree of protection, at the time of writing, from any number of current malware loaders that are using the ISO image technique to achieve initial code execution. The nature of the separate filesystem within the ISO presently prevents it from being marked as being from the Wild Wild West World Wide Web.
In a continuation of my desire to write really lightweight software that doesn’t add to the undesirable background bloat running on computers, I set about in June-ish to write something to improve upon a VBScript-Scheduled-Task-and-shutdown.exe gaffer tape of a solution to forcing a full shutdown when a computer is idle that I had previously cobbled together.
Power management in Windows is mature and capable, for sure, but what is less obvious is how to, on shared fixed desktop computers, actually trigger a proper shutdown and not just put idle machines to sleep. Hibernation is an option, of course, but the relentless increase in complexity of Windows brings to mind the other, stability-related, benefits of regular proper restarts.
So, then, we want something that:
identifies when no-one is interactively signed in
waits a configurable amount of time
if still no-one has signed in in that time, shut down properly
Additionally, because this unavoidably must run with high permissions and regularly assess signed in users in the background, it should be a Windows service that is as lightweight and simple as possible. Reduced resource usage (RAM, CPU time in background) so we can shut down and have reduced resource usage (of electrical power). I can see the beauty of it already!
Like all my lightweight, C(++) Win32 projects, it is officially experimental as I am using these projects to learn how to write this kind of code properly. Any suggestions and improvements are gratefully received.
Despite the inexorable march towards running all workloads in the cloud, I see some specific advantages in maintaining some on-premises servers where this makes sense. Especially in a small scale environment like the one I am responsible for, this lets me do Interesting Things with my skill set and at small scale, only because I have full control over on-prem kit.
One of the options for backing up Hyper-V workloads I am looking at is Microsoft Azure Backup Server (MABS) v3. On a brand new deployment (Windows Server 2019), following Microsoft’s guide, I ran into issues with the MABS installer.
At the point of connecting to the Vault above, it would take a long time to “validate credentials” and then:
Invalid vault credentials provided. The file is either corrupt or does not have the latest credentials associated with recovery service. ID 34513
I found a way to work around this — we need to slipstream an updated version of the Microsoft Azure Recovery Service (MARS) Agent into the MABS installer before we run it.
Tidy Up First
If you have a messy server after some failed install attempts, roll back the VM if possible, or uninstall all MABS and MARS components with Add/Remove Programs.
Also, use the MMC certificates snap-in in Local Computer mode to remove any stale vault credential certificates.
To do, this launch mmc.
We will Add/Remove Snap-ins, and choose Certificates, Local Computer.
Remove any CB_ certificates from previous runs to avoid any possibility of confusion when the registration process runs again.
Take care to ensure you understand what you are doing before deleting certificates and keys. Do not delete anything you are not certain is unused and related to MABS. I cannot take responsibility for your loss if you follow this guide and have issues.
In the Azure Portal, go to your backup vault and check Backup Management Servers and Protected Servers, removing any registrations from previous failed installs, so we are installing into the vault with a clean state. Alternatively, create a new vault. I unfortunately ended up with my MABS server in Protected Servers and had to delete it. Ultimately it will be registered as a Backup Management Server, not a Protected Server.
The Workaround — Slipstream Updated MARS into MABS Installer
We will have the .exe and 7 .bin files. Run the .exe to extract the bin files. The install “media” in this case has now been extracted to C:\System_Center_Microsoft_Azure_Backup_Server_v3\System Center Microsoft Azure Backup Server v3.
Before we run the MABS setup wizard, we need to slipstream in the updated MARSAgentInstaller. Do not run the MARSAgentInstaller separately – we must have it invoked by the MABS wizard at the right time and in the correct context. If MARS is already installed when we try to install MABS, it will be unhappy and refuse.
I turned off TLS on the client and the receiving Graylog Input, thinking it might be some TLS-related issue, to the same error.
To cut a long story short, decimal 71 and decimal 69 are ASCII codes for capital G and capital E — the first two bytes of an HTTP request that the Winlogbeat client was making to the Graylog input. Clearly the input is not expecting to receive ASCII “GE” to start the request!
It turns out the Graylog beats input desires the logstash format, not elasticsearch. I had been ignorant in just modifying the example config in the output.elasticsearch section, when this is not what Graylog wants.
I commented out the entire output.elasticsearch section and moved that configuration (hosts and the ssl options) into an output.logstash YML node.
This was unclear enough to me that I thought connecting the error messages above with this solution may prove useful for someone else who has the issue.
With a relatively recent Azure AD hybrid directory under our belts, we decided at work not to use the older Azure AD Connect tool and instead use the newer Azure AD Connect Cloud Sync. It’s lighter weight, doesn’t require a SQL database — lots of reasons to love it.
It does appear that, juuuust in time for our deployment, password writeback is supported, in preview.
However, I struggled to follow the official instructions to enable it, as the cmdlet did not seem to be available after importing the DLL.
Set-AADCloudSyncPasswordWritebackConfiguration : The term 'Set-AADCloudSyncPasswordWritebackConfiguration' is not
recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if
a path was included, verify that the path is correct and try again.
At line:1 char:1
+ CategoryInfo : ObjectNotFound: (Set-AADCloudSyn...ckConfiguration:String) , CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException
A little bit of investigating revealed that the DLL does indeed export the cmdlet, so what is going on?
I tried to run the above in PowerShell 7. It imported the cmdlet, but hit an issue with running it when importing its required libraries.
My workaround is to use PowerShell 7, but import the module with the -UseWindowsPowershell compatibility switch.
I have been getting back into the swing of building things just for fun and for exploration. I think a pressure can emerge that the things we create have to mean something, have to hit some mark of quality to be worthy of pursuing at all. I think that is a mistake, especially in that it discourages you from being open to areas where you don’t already have great expertise. So, here I am, putting into practice rejecting that pressure.
Continuing my theme of trying to work with lower-level APIs and with unmanaged languages like C and C++, I have developed a very simple client for Windows’ Volume Shadow Copy service, that allows me to create a shadow copy of a volume, copy some files in a folder to a destination, and then release the shadow copy.
I can see a use for this as part of a very low-tech backup solution where a drive is (most of the time) physically disconnected, and where you want to keep the technology stack as simple as humanly possible for the greatest flexibility in disaster recovery scenarios — BitLocker for external drives (compatible even with Windows client systems), and a bunch of VHDX files on an NTFS volume, copied there using VSS so you don’t have to bring your VMs down.
A big disclaimer is prominently offered — this is not production quality code. My discipline with the responsibility of memory management and other lower-level concepts is “emerging”, to use a euphemism.
Still, I thoroughly enjoyed this — it was challenging for where I currently am, but achievable. You can’t improve at something if you don’t let yourself produce output that wouldn’t perhaps yet meet your highest quality standards. (And goodness knows there is plenty of production code out there that never met those standards before it was relied upon by the world.) The perfect shall not be allowed to be the enemy of personal growth and development.
So, here is ShadowDuplicator, your very untested, extremely rudimentary VSS snapshot based backup client. Even if it’s just a workaround for a lack of vssadmin create shadow on client operating systems, it’s something. 😉