Windows authentication bypasses small flaws that will make BitLocker disk encryption a big defeat

Windows computers that use BitLocker and join a domain should be patched as soon as possible

Lusien Constantine (Lucian Constantin) 2015-11-14 translation: Purpleendurer

Ian Hacken Ian Haken at the Black Hat European security conference in Amsterdam, November 13, 2015, Lusien Constantine (Lucian Constantin)

Companies relying on Microsoft BitLocker to encrypt employees ' computer hard drives should immediately install the latest Windows patches. A researcher revealed a simple Windows authentication circumvention method, which makes data in BitLocker encrypted drives dangerous. The vulnerability was fixed earlier this week.
Ian Hacken Ian Haken, a software security test researcher at Synopsys, demonstrated the attack at the Black Hat European security Conference held in Amsterdam in Friday (note: 2015-11-13). This issue affects Windows computers that are connected to the domain, which is a common configuration in the corporate network.
When you use domain-based authentication on Windows, the user's password is checked by the computer acting as the domain controller. However, in some cases, for example, when a laptop is out of the network and cannot connect to a domain controller, authentication relies on the local credentials cached on the machine.
To prevent an attacker from connecting a stolen, lost, or unattended laptop to a different network and creating a pseudo-domain controller to accept another password for unlocking, the authentication protocol verifies the individual computer passwords that the computer itself registers on the domain controller.
This additional check does not occur when the controller is unable to connect because the developer of the Protocol assumes that the attacker cannot alter the user's password stored in the local cache. However, Harken came up with a way to do this-and if the process could be automated, it would only take a few seconds.
First, the attacker establishes an analog domain controller whose name is the same as the domain controller that the laptop computer should be connected to. He then creates the same user account as the laptop user on this emulated domain controller and creates an expired password for it.
When the authentication mechanism tries to reconcile the password of an attacker on the laptop, the domain controller notifies the laptop that the Windows password has expired and the user is automatically prompted to change the password. This process occurs before the computer checks the password for the controller registration.
At this point, the attacker could create a new password on the laptop, replacing the original password in the local credential cache.
Because there is no machine password for the laptop on the controller, logging on to a malicious domain controller will still fail. However, the attacker could disconnect the laptop from the network and force the verification process back to local authentication, which is done because only the cached user's password needs to be validated.
This is a logical flaw that has been present in the authentication protocol since Windows 2000, the researcher said. However, physical access as part of the Windows threat model will not work because in this case an attacker could boot from an alternate source such as a Linux CD to access the data.
When BitLocker introduced Windows Vista, everything changed. Microsoft's full-disk encryption technology, which is a feature of professional and enterprise versions of Windows, is designed to protect data when a computer is stolen or lost-in other words, for unauthorized access to physical information.
The BitLocker data encryption key is stored in the TPM (Trusted Platform module, Trusted Platform Module), which is a secure hardware component that performs cryptographic operations. After BitLocker is activated for the first time, the key is enabled from the TPM only after the same process is started.
Password Authentication is performed at all stages of the boot process, so for a BitLocker-enabled laptop, the data stored on the drive cannot be read if an attacker initiates physical access from another operating system. In this case, the only thing an attacker could have exploited was to get the system up and running, open the encryption key, and then bypass Windows authentication to access the data, which is the Harken attack.
Microsoft fixed the flaw in Tuesday and released the appropriate security bulletin ms15-122.
Harken said the attack showed that we need to constantly re-examine the theory that we felt was reliable for security, Harken said.
BitLocker provides the Enable option for pre-boot authentication, and you can use a PIN or USB drive to store special keys in addition to the TPM. However, such a configuration is difficult for businesses because it can cause frictions and disagreements among users, and makes it difficult for administrators to remotely administer computers, Harken said.
Microsoft acknowledges in the documentation that pre-boot authentication is "unacceptable in the modern it world, that users expect their devices to be on and off, and that it requires the PC to be connected to the network".
　　
English Original: http://www.networkworld.com/article/3005179/ Bitlocker-encryption-can-be-defeated-with-trivial-windows-authentication-bypass.html
　　

Windows authentication bypasses small flaws that will make BitLocker disk encryption a big defeat