A new trend in adware and unwanted program purveyors is to install protection software that makes it more difficult for Windows users to run their security programs and clean infections. This was seen with the SmartService rootkit that blocked AV software from running and now with a protection program being called CertLock.

Since the end of May, security forum helpers have noticed reports that people are not able to install and run security programs on their infected computers. When they try to run the programs, they are greeted with an alert that states that the publisher has been blocked from running on the computer.

It turns out that this is being caused by CertLock disallowing a security vendor's certificate on the affected computer so that Windows does not allow the program to run. 

CertLock disallows security vendor certificates

Being commonly detected as Ceram or Wdfload by anti-virus vendors, CertLock is distributed by unwanted programs bundles, such as miners. Once installed, CertLock will block a security vendor's certificate by adding them to a special Windows registry key. This causes Windows to not execute any programs that are signed with that certificate.

CertLock blocks a certificate by creating a subkey named using the thumbprint of the certificate it wants to block to the following key:

HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\

As an example, one of ESET's certificates has a thumbprint of F83099622B4A9F72CB5081F742164AD1B8D048C9. To block this certificate, CertLock will create a Registry key called: 

HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\F83099622B4A9F72CB5081F742164AD1B8D048C9

Under this key will be a single BLOB value that contains the certificate information. You can see an example of the registry key used to block the ESET certificate below.

If a certificate is added to the Disallowed list, when a user tries to run a program that is signed by this certificate they will be greeted with an error that states "The publisher has been blocked from running software on your machine". You can see an example of the ESET installer being blocked using this method below.

Blocked ESET Installer
Blocked ESET Installer

While blocking certificate prevents signed installers from running, it also prevents already installed programs that use the blocked cert from executing as well. For example, when Malwarebytes' code-signing certificates are blocked, users are greeted with errors when they try to run the program. These errors state:

Unable to start
Unable to connect the Service.

or

Error

Runtime Error (at 49:120):

Could not call proc.

You can see examples of these errors below:

Unable to connect the Service
Unable to connect the Service Error
Malwarebytes 49:120 Error
Malwarebytes 49:120 Error

This trojan really does not like Avast

While CertLock already disallows the use of the AVAST certificate, it also goes a step further to make sure Avast is unable to run. It does this by pointing many Avast.com hostnames to 127.0.0.1 using the Windows HOSTs file so that the computer cannot connect to them.

CertLock generates the list of Avast hosts to block by downloading the files.avast.com/iavs9x/servers.def file. This file contains a list of hostnames associated with Avast security program. It then parses this file and adds them to the Windows HOSTS file as shown below.

Modified HOSTS File
Modified HOSTS File

By adding the hostnames to the HOSTS file and pointing them to 127.0.0.1, it effectively blocks the computer from reaching these servers.

How to remove Certificates Disallowed by CertLock

ToolsLib.com co-administrator and Malwarebytes AdwCleaner developer Jérôme.B has created a tool called AVCertClean that will scan the Disallowed registry key for legitimate blocked keys and remove them. To use the tool, simply download and execute it. The program will then automatically remove blocked certificates

AVCertClean
AVCertClean

When the program has finished, it will display a log that lists the certificates that were cleaned by AVCertClean.

AVCertClean Log
AVCertClean Log

Now that the certificates are no longer being blocked, users can install and run their security programs in order to clean their computer. In some situations, user's may need to restart the application in order to get them to run.

For example, for Malwarebytes to run after cleaning the certs, users should go into the Windows Service Manager (services.msc) and restart the Malwarebytes Service.

 

IOCs

Hashes:

b1cbe0ee129bc96cc3e3d2aa4bc2ce3f6b7403045bd0ffc8956b7b7af4d070f5 - Installer (Password Protected)
b529ca4dd148fdfcee0c1f267bc6821cc5168c121363fa690536a72e0f447c19 - CertLock (Thx Aura)

Registry Entiries Associated with CertLock:

HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\03D22C9C66915D58C88912B64C1F984B8344EF09
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\0F684EC1163281085C6AF20528878103ACEFCAAB
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\1667908C9E22EFBD0590E088715CC74BE4C60884
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\18DEA4EFA93B06AE997D234411F3FD72A677EECE
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\2026D13756EB0DB753DF26CB3B7EEBE3E70BB2CF
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\249BDA38A611CD746A132FA2AF995A2D3C941264
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\31AC96A6C17C425222C46D55C3CCA6BA12E54DAF
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\331E2046A1CCA7BFEF766724394BE6112B4CA3F7
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\3353EA609334A9F23A701B9159E30CB6C22D4C59
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\373C33726722D3A5D1EDD1F1585D5D25B39BEA1A
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\3850EDD77CC74EC9F4829AE406BBF9C21E0DA87F
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\3D496FA682E65FC122351EC29B55AB94F3BB03FC
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\4243A03DB4C3C15149CEA8B38EEA1DA4F26BD159
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\42727E052C0C2E1B35AB53E1005FD9EDC9DE8F01
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\4420C99742DF11DD0795BC15B7B0ABF090DC84DF
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\4C0AF5719009B7C9D85C5EAEDFA3B7F090FE5FFF
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\5240AB5B05D11B37900AC7712A3C6AE42F377C8C
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\5DD3D41810F28B2A13E9A004E6412061E28FA48D
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\7457A3793086DBB58B3858D6476889E3311E550E
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\76A9295EF4343E12DFC5FE05DC57227C1AB00D29
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\775B373B33B9D15B58BC02B184704332B97C3CAF
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\872CD334B7E7B3C3D1C6114CD6B221026D505EAB
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\88AD5DFE24126872B33175D1778687B642323ACF
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\9132E8B079D080E01D52631690BE18EBC2347C1E
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\982D98951CF3C0CA2A02814D474A976CBFF6BDB1
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\9A08641F7C5F2CCA0888388BE3E5DBDDAAA3B361
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\9C43F665E690AB4D486D4717B456C5554D4BCEB5
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\9E3F95577B37C74CA2F70C1E1859E798B7FC6B13
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\A1F8DCB086E461E2ABB4B46ADCFA0B48C58B6E99
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\A5341949ABE1407DD7BF7DFE75460D9608FBC309
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\A59CC32724DD07A6FC33F7806945481A2D13CA2F
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\AB7E760DA2485EA9EF5A6EEE7647748D4BA6B947
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\AD4C5429E10F4FF6C01840C20ABA344D7401209F
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\AD96BB64BA36379D2E354660780C2067B81DA2E0
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\B8EBF0E696AF77F51C96DB4D044586E2F4F8FD84
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\CDC37C22FE9272D8F2610206AD397A45040326B8
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\D3F78D747E7C5D6D3AE8ABFDDA7522BFB4CBD598
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\DB303C9B61282DE525DC754A535CA2D6A9BD3D87
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\DB77E5CFEC34459146748B667C97B185619251BA
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\E22240E837B52E691C71DF248F12D27F96441C00
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\E513EAB8610CFFD7C87E00BCA15C23AAB407FCEF
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\ED841A61C0F76025598421BC1B00E24189E68D54
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\F83099622B4A9F72CB5081F742164AD1B8D048C9
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\FBB42F089AF2D570F2BF6F493D107A3255A9BB1A
HKLM\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates\FFFA650F2CB2ABC0D80527B524DD3F9FC172C138
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce\[computer_name]	%temp%\[temp_name].tmp.exe

Files Associated with CertLock:

%temp%\[temp_name].tmp.exe

Disallowed Certificates (Thumbprints):

Security Vendor Thumbprint
AVAST AD4C5429E10F4FF6C01840C20ABA344D7401209F
AVAST DB77E5CFEC34459146748B667C97B185619251BA
AVG 3D496FA682E65FC122351EC29B55AB94F3BB03FC
AVG AB7E760DA2485EA9EF5A6EEE7647748D4BA6B947
AVG Technologies E513EAB8610CFFD7C87E00BCA15C23AAB407FCEF
Adaware 9132E8B079D080E01D52631690BE18EBC2347C1E
Avira A1F8DCB086E461E2ABB4B46ADCFA0B48C58B6E99
BitDefender 18DEA4EFA93B06AE997D234411F3FD72A677EECE
BitDefender ED841A61C0F76025598421BC1B00E24189E68D54
BullGuard A5341949ABE1407DD7BF7DFE75460D9608FBC309
Bullguard 76A9295EF4343E12DFC5FE05DC57227C1AB00D29
Checkpoint Software 5240AB5B05D11B37900AC7712A3C6AE42F377C8C
Comodo 03D22C9C66915D58C88912B64C1F984B8344EF09
Comodo 872CD334B7E7B3C3D1C6114CD6B221026D505EAB
CurioLab 9E3F95577B37C74CA2F70C1E1859E798B7FC6B13
Doctor Web 4420C99742DF11DD0795BC15B7B0ABF090DC84DF
Doctor Web FFFA650F2CB2ABC0D80527B524DD3F9FC172C138
ESET A59CC32724DD07A6FC33F7806945481A2D13CA2F
ESET F83099622B4A9F72CB5081F742164AD1B8D048C9
Emsisoft 4C0AF5719009B7C9D85C5EAEDFA3B7F090FE5FFF
Emsisoft 5DD3D41810F28B2A13E9A004E6412061E28FA48D
F-Secure 0F684EC1163281085C6AF20528878103ACEFCAAB
FRISK 1667908C9E22EFBD0590E088715CC74BE4C60884
GData 2026D13756EB0DB753DF26CB3B7EEBE3E70BB2CF
K7 Computing 42727E052C0C2E1B35AB53E1005FD9EDC9DE8F01
K7 Computing 7457A3793086DBB58B3858D6476889E3311E550E
Kaspersky 3850EDD77CC74EC9F4829AE406BBF9C21E0DA87F
Kaspersky D3F78D747E7C5D6D3AE8ABFDDA7522BFB4CBD598
Malwarebytes 249BDA38A611CD746A132FA2AF995A2D3C941264
Malwarebytes B8EBF0E696AF77F51C96DB4D044586E2F4F8FD84
McAfee 775B373B33B9D15B58BC02B184704332B97C3CAF
McAfee 88AD5DFE24126872B33175D1778687B642323ACF
PC Tools 4243A03DB4C3C15149CEA8B38EEA1DA4F26BD159
Panda FBB42F089AF2D570F2BF6F493D107A3255A9BB1A
SUPERAntiSpyware 373C33726722D3A5D1EDD1F1585D5D25B39BEA1A
Safer Networking 982D98951CF3C0CA2A02814D474A976CBFF6BDB1
Symantec 31AC96A6C17C425222C46D55C3CCA6BA12E54DAF
Symantec AD96BB64BA36379D2E354660780C2067B81DA2E0
ThreatTrack Security 9C43F665E690AB4D486D4717B456C5554D4BCEB5
ThreatTrack Security DB303C9B61282DE525DC754A535CA2D6A9BD3D87
Total Defense E22240E837B52E691C71DF248F12D27F96441C00
Trend Micro 331E2046A1CCA7BFEF766724394BE6112B4CA3F7
Trend Micro CDC37C22FE9272D8F2610206AD397A45040326B8
Webroot 3353EA609334A9F23A701B9159E30CB6C22D4C59
Webroot 9A08641F7C5F2CCA0888388BE3E5DBDDAAA3B361