How to Fix KMODE_EXCEPTION_NOT_HANDLED (cng.sys) BSOD on Windows 10?

by Olivia Morelli - -


Issue: How to Fix KMODE_EXCEPTION_NOT_HANDLED (cng.sys) BSOD on Windows 10?

Hello. I’m a new Windows 10 user and I’m already regretting that I’ve switched to this OS. I’ve upgraded from Windows 8 to 10 few days ago, but now I get a BSOD every time I start the system. The error says KMODE_EXCEPTION_NOT_HANDLED (cng.sys). Please help!

Solved Answer


KMODE_EXCEPTION_NOT_HANDLED (cng.sys) is a BSOD error, which emerges on Windows 10 OS exceptionally. While it initially emerged in 2015, some people still confront this lock screen, so apparently Microsoft hasn’t yet eliminated the culprit. According to some programmers, this BSOD is triggered by a conflict between Window OS and the Realtek  driver. However, similarly to other blue screen errors, this one may also be caused by registry corruption, software compatibilities or malware.

While analyzing people’s reports on Microsoft forum, we’ve found false claims that removal of cng.sys is the easiest solution. BUT: do not use this recommendation because cng.sys is one of the critical Windows system file, meaning that it’s misplacement, removal or damage may cause further hardware and software incompatibilities. Consequently, the PC may crash without leaving you the ability to fix it without the help of professional technicians.

Typically, KMODE_EXCEPTION_NOT_HANDLED (cng.sys) BSOD occurs when starting the system after a shutdown or hibernate, but not restarting. The stop error freezes the screen and prevents the system from booting up normally. Nevertheless, in some of the cases, people managed to resolve the issue by simply forcing the system to shut down and then boot into Safe Mode. This may happen if the system has started malfunctioning due to a temporary failure. If, however, the KMODE_EXCEPTION_NOT_HANDLED (cng.sys) error is triggered by driver failure, software incompatibility or damaged registries, you will need to fix the problem by performing the methods provided below.

Method 1. Reinstall Realtek driver

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  • Right-click on Win key and select Device Manager.
  • When the Device Manager window opens, expand Network controllers folder, right-click on Realtek driver and select Uninstall. If a confirmation window pops up, click OK to proceed. In some rare cases, users are required to enter Administrator password, so if you have received such permission, make sure that you type in the right password.
  • After that, expand Sound, video, and game controllers and uninstall Realtek driver as well.
  • Once the process is finished, restart your PC.
  • Now you have to re-install the drivers that you have removed before. To do this, go to the Device Manager again.
  • Click Action tab on the toolbar.
  • Select Scan for Hardware Changes and let the system detect and install the missing driver automatically.
  • If for some reason this process ends up with the failure, go to the manufacturer’s website and download the drivers manually.

Method 2. Scan the system for damaged Registry keys

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Damaged, misplaced or corrupted Registry Entries is the number one problem, which triggers most of the errors that people encounter on Windows 10 OS. Therefore, if driver removal did not help you to fix KMODE_EXCEPTION_NOT_HANDLED (cng.sys) BSOD error, install Reimage or another powerful PC optimization tool and run a full system scan with it. By the way, running the scan with this tool will also let you know if your PC is malware-free. As we have pointed out, virus or malware infection may also influence the emergence of BSOD during startup.

Method 3. Turn Off Fast Startup

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Several people have approved that disabling Fast Startup has helped them to resolve the cng.sys bug. Therefore, if the previous methods did not help, then this one is worth trying:

  • Right-click Win key and select Control Panel.
  • Open Power Opwions and click Choose what the power buttons do on the left pane.
  • Select Change settings that are currently unavailable under Define power buttons and turn on passwords.
  • If UAC window opens, click Yes to proceed.
  • Find Shutdown settings and uncheck Turn on fast startup box.
  • Click Save changes and close the window you are currently in.

Hopefully, these steps have helped you to fix cng.sys error. If, after all, you cannot get rid of this BSOD, you may also try to restore the system using the Previous Restore Point or try a clean install.

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About the author

Olivia Morelli
Olivia Morelli - PC & Mac repair expert

Olivia Morelli is a young, but a perspicacious IT expert who is currently just a year away from a Bachelor’s Degree in Software Systems. Her primary passion is cyber security, however, thanks to her detailed understanding of computer networks, operating systems and hardware, she can find a fix for any PC or Mac issue...

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