Password protection and other security measures for MS Access database_问答_开发者

I have be开发者_如何学编程en asked to secure an Access database at the highest level possible, and something tells me password protecting the file is not sufficient. We have really sensitive data and I need to protect it to the greatest extent possible. Any ideas?

This has been an issue that I have had for several years with Access 2003. We set a Database Password on the database to lock it down so users would need the password to access it. Not necessarily the best option and kind of a pain.

Since you are using MS Access 2007 you might want to check out want Microsoft says are database protection options.

First, when discussing security, we have to define the threat model.

Common threats are:

Unauthorized access of data: Someone that shouldn't be able to read data, is able to read data.
Unauthorized modification of data: Someone that shouldn't be able to modify data, is able to modify data
Unauthorized destruction/corruption of data: Someone is able to vandalize the database
Privilege escalation: Someone who should be able to read or write some of the data, is able to read or write more than intended
Data exfiltration: someone who should be able to read some data is able to copy large amounts of data and move it to an external (or less protected) system.
Malware insertion: someone is able to insert malicious code into the application

The main defense for Access, as discussed, is encrypting the database using a database password. When using an accdb file, this generally offers sufficient protection against unauthorized access and modification of the data. This is a "one privilege fits all" approach, there is one password, if you have it, you have all privileges and can read, write, and insert components at will. Also, when you have write access to the file, but not the password, you are able to damage or delete the file.

A level higher is securing the Access file: using a secure file server to only serve the file to those who should have access to it. This comes with practically all benefits of encryption, and protects against destruction too, as unauthorized users cannot access the file. This also allows us to revoke rights to that folder, assuming the user hasn't made a copy.

If we want to work with user rights, we can separate the file into a front-end file, which does not contain privileged data, and multiple backend files, and secure these files separately, by either using a different password for each file, or storing them on separately secured locations. Again, secure locations offer the additional benefit of protecting against destruction.

Since Access requires users to have write permission to the file (for placing locks) to have read access, however, we can't easily separate read and write permissions this way. One approach I've seen used is using a "shadow folder", where a virtual folder is created for read users, and upon accessing the folder, the most recent database file is placed in it, and overwritten each time. Setting this up, however, is nontrivial.

Another approach which is very common is trying to use VBA to limit which actions users can take, and allowing them only to open specific forms and take specific actions on them. This is possibly combined with tricks like disabling the bypass key, and/or creating a compiled copy (accde/mde) without the original code. However, these will only stop novice attackers, and can practically always be bypassed, either by using a non-Access program to read the data (which will ignore any restriction imposed by VBA), allowing the bypass key through COM, disabling VBA altogether on the machine, etc. A compiled database only makes it impossible to view and modify the code, not the data, and this also can be bypassed by experts by manually reconstructing the code (example commercial service that offers this). Thus, while this may look like proper security at first glance, it has severe flaws.

Compiling the code is useful when combined with signing the code, to protect against unauthorized malware insertion. Since a decompiled, modified and then recompiled copy won't have a valid signature, assuming the attacker can't access the trusted certificate used to sign the code, and systems can be configured not to open compiled databases without that signature, this can help detect malicious modification of the database.

If we want to have separate user privileges, but cannot enforce this using separately secured folders, an option is to have separately encrypted backends with different keys. For usability purposes, we can use a key encryption key to have a separate password for each user, and have that password grant access to the backends which the user is allowed to use. I've created a sample of a database that uses key encyption keys for this Q&A, but nowadays I'd make some changes, such as using a single front-end with both the KEKs and linked tables to the encrypted databases, and using the CNG API for fast encryption in VBA.

Note that some of these options add a lot of complexity, and none properly protects against data exfiltration (which is an increasing threat in the country + sector I work in). Often, it's a lot more simple, in terms of infrastructure, management, etc. to use a different back-end than Access. This can still allow you to use Access as the front end, so users might not even notice a change, but management of permissions is determined by the back end, which can either be secured by using different passwords for each users, or, in case of SQL server, by linking security to an AD domain (SSPI).

In SQL server, we can also add logging, restrict fetching large datasets by only granting rights to stored procedures and limit the amount of requests over time, to mitigate data exfiltration. However, the added complexity this brings to using Access as a client often makes choosing a different client more sensible, if you only use stored procedures linked tables are not available and Access tends to make more requests than necessary.

Note that when choosing to use a different back-end, it is still recommended to compile and sign the Access database to mitigate malware insertion, which is not dependent on the back-end used.

Bonuses:

What about user-level security? That was a technology specifically intended to offer per-user read and write rights, and separate rights for modifying the database and managing users. Unfortunately, it was insecure and there are many tools out there to remove it, and it only applies to the mdb and mde database formats, so is not of any use.

And, of course, you can also secure the user by securing the environment that Access runs in. I've seen a deployment where users are only allowed to access resources in a virtual environment that is behind a firewall disallowing all internet access, is limited to only opening this specific database, doesn't allow storage devices, and doesn't share the clipboard with the main environment. That allows you to have a secure database by using VBA, but severely limits usability of the database (especially the copy-paste limitation frustrates users, but copying and pasting could be used for data exfiltration).

I would suggest you put it on a file server and have a strict access control list.

In the database force users to log in then add triggers to write out audit info when a record changes (with the user info,date/time).