Cryptographic Services failed while processing the OnIdentity() call

 

"Microsoft Link-Layer Discovery Protocol" binary is \Windows\system32\DRIVERS\mslldp.sys
Its config registry key is HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MsLldp

During backup a VSS process running under NETWORK_SERVICE account calls cryptcatsvc!CSystemWriter::AddLegacyDriverFiles(), which enumerates all the drivers records in Service Control Manager database and tries opening each one of them. , The function fails on MSLLDP record with "Access Denied" error.

Turned out it fails because MSLLDP driver's security permissions do not allow NETWORK_SERVICE to access the driver record.

The binary security descriptor for the record is located here:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MsLldp\Security

It should be modified, I used SC.EXE and Sysinternals' ACCESSCHK.EXE to fix it.

Using Command Prompt (Admin)

The original security descriptor looked like below:

>accesschk.exe -c mslldp

mslldp
RW NT AUTHORITY\SYSTEM
RW BUILTIN\Administrators
RW S-1-5-32-549 <- these are server operators
R NT SERVICE\NlaSvc

No service account is allowed to access MSLLDP driver

The security descriptor for the drivers that were processed successfully looked this way:

>accesschk.exe -c mup

mup
RW NT AUTHORITY\SYSTEM
RW BUILTIN\Administrators
R NT AUTHORITY\INTERACTIVE
R NT AUTHORITY\SERVICE <- this gives access to services

How to add access rights for NT AUTHORITY\SERVICE to MSLLDP service:

1. Run: SC sdshow MSLLDP

You'll get something like below (SDDL language is documented on MSDN):

D:(D;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BG)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;SY)(A;;CCDCLCSWRPDTLOCRSDRCWDWO
;;;BA)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;SO)(A;;LCRPWP;;;S-1-5-80-3141615172-2057878085-1754447212-2405740020-3916490453)S:
(AU;FA;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;WD)

2. Run: SC sdshow MUP

You'll get:

D:(A;;CCLCSWRPWPDTLOCRRC;;;SY)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BA)(A;;CCLCSWLOCRRC;;;IU)(A;;CCLCSWLOCRRC
;;;SU)S:(AU;FA;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;WD)

3. Take NT AUTHORITY\ SERVICE entry, which is (A;;CCLCSWLOCRRC;;;SU) and add it to the original MSLLDP security descriptor properly, right before the last S:(AU... group.

4. Apply the new security descriptor to MSLLDP service :

sc sdset MSLLDP

D:(D;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BG)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;SY)(A;;CCDCLCSWRPDTLOCRSDRCWDWO
;;;BA)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;SO)(A;;LCRPWP;;;S-1-5-80-3141615172-2057878085-1754447212-2405740020-3916490453)
(A;;CCLCSWLOCRRC;;;SU)S:(AU;FA;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;WD)

5. Check the result:

>accesschk.exe -c mslldp

mslldp
RW NT AUTHORITY\SYSTEM
RW BUILTIN\Administrators
RW S-1-5-32-549
R NT SERVICE\NlaSvc
R NT AUTHORITY\SERVICE