"Maliciousadmin" user doesnt have access to encrypted file - Create by Other user Here are some of the POC which I simulated in my test environment. In order to decrypt this Master key we need to conduct bruteforce attack. Private key is encrypted with Master key. Using this tool, you will be able to identify EFS encrypted files throughout disk, and find following two important keys : Using 'admin' credentials - Install a tool "Advanced EFS Data Recovery Tool" - Its commercial () ( This is quite complex process but yes you can definitely follow the steps and attempt to recover your keys )Ģ. Using 'admin' credentials attempt to execute Mimikatz::Crypto commands mentioned below Now in this case, there are two approaches,ġ. In this case 3, it becomes a challenge, because you dont have valid password for the account ' Administrator' and hence it wont be possible to access EFS encrypted files directly even via other administrator user name ' admin' This is of course simple trick.Ĭase 2 : I also tried changing 'administrator' password from account 'admin' and it works, you can just login with your new password and still be able to access EFS encrypted files - So no dependencies even if password is changed.Ĭase 3: What if because of some reason, you are not able to extract windows password from system memory, or what if system access is configured via SmartCard, you may not find domain passwords/local administrator passwords in system memory. Authenticate over SMB and access EFS encrypted files just like normal files. Extract system passwords from memory with Mimikatz, and get the password for account ' Administrator' ( Password for user which encrypted the file) ,Ģ. Using Cipher command to know information about encrypted fileĬase 1 : Once you have administrator level access to the system, I would suggest,ġ. Step 1 : Using ' Cipher' command in Windows, you can encrypt / decrypt files, view encrypted file information and use it further for your attacks, I have executed below command with user 'admin' which is administrator account on the system and found that files are encrypted by user named 'Administrator' - That's what important to us! In your penetration testing, you must get an administrator level access the system for decryption of EFS files. Now its clear, that only user who encrypted the file can decrypt it!. Encrypted File System (EFS) is a Microsoft Windows feature for encrypting files nad folders on NTFS drives.Įncrypting folder name 'Encrypt' with user 'Administrator' Recently came across scenario on decryption of EFS ( Encrypted File System) encrypted files.
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