Re: PcwRunAs Password Obfuscation Design Flaw

["Thor (Hammer of God)" <thor () hammerofgod com>]

You've well-articulated a problem most (if not all) of the implementations I've seen just dance over.   The application 
accomplishes the encryption requirements stipulated by policy or regulation, but the key is easily available to the 
application and of course to attackers.  

I have no idea what mitigation techniques are available for PHP, but in .NET/Win applications there are a couple of 
"first step" attempts to at least address the problem.  First you've got DPAPI, which in its simplest form is an API 
that allows the application to encrypt/decrypt data by way of keys stored in the system certificate store which is 
protected by a different set of credentials.  The attacker would have to get system to get to the keys.  Of course, if 
the attacker could alter code as you've outlined, then they could very well just use the API to decrypt data without 
worrying about getting the keys themselves.  The problem with DPAPI is that it is system-based.  The data encrypted by 
that system can only be decrypted by that system.  That won't work in distributed environments, and it can be 
problematic in system failure scenarios.

To get passed single-machine issues, there is another method called DKM, which as the name infers is a distributed key 
management system based on AD and the machines' membership is appropriate groups given access to the keys.  So in a 
similar fashion, keys are protected by secondary credentials at the machine level.  Again, this requires an attacker to 
gain system access to get the keys, but again, gives an attacker with file-level access where code can be changed 
access to the procedure calls to get the data if they have to. 

It is a very difficult problem to solve, but it all comes down to risk management.   If you are protecting against 
off-line attacks or attacks from other systems, DPAPI or DKM will definitely help.  If you are protecting against 
attacks where SYSTEM access is granted, it gets far more difficult (one may even say quite improbable) to protect the 
keys.  

What I've been doing myself is a bit different, but it ultimately suffers from the same potential issues:  As part of 
my TGP "suite,"  I've extended functionality to WinMobile so that data encrypted on the PC can be exchanged and 
decrypted on the phone.  It's pretty cool actually...  to get around the key management issues, I wrote an API where 
the devices authenticate to, and use certificates to gain access to the encrypted keys on a centralized key store.   On 
the phone, the calls are made each time keys are needed.  On my web servers, the call is actually made on application 
startup, storing the keys in memory.    At any time one becomes aware of some breach, you can cut off access to the 
keys.  Not ideal of course, but it works.

I'm not worried about the BSOD scenario.  The remote attacker would have to cause a BSOD, and then somehow access the 
dump.  In production systems, the page files are typically kept on another drive (well, maybe not "typically" but that 
is up to the admins) in which case the dump won't exist.   But to your point, I just looked at my own web VM, and it is 
indeed set to do a full dump to the system drive.   I still don't think there is enough of a risk of that type of 
breach to warrant changing the paradigm from system-only access to keys in memory.

I too would be interested in hearing what processes others are using to address this. 

t



> -----Original Message-----
> From: full-disclosure-bounces () lists grok org uk [mailto:full-disclosure-
> bounces () lists grok org uk] On Behalf Of b
> Sent: Tuesday, March 27, 2012 6:16 PM
> To: full-disclosure () lists grok org uk
> Subject: Re: [Full-disclosure] PcwRunAs Password Obfuscation Design Flaw
>
> So this brings up an interesting problem to tackle:
>
> How can you encrypt things for use by applications such as service account
> credentials for authentication to other systems and database access
> credentials on disk in such a way that the application can obtain the
> encrypted information without prompting the end user for a decryption
> passphrase and an attacker with local filesystem access cannot obtain the
> encryption key to the credentials by simple computation (like if you had the
> encryption key calculated based on some static/easily guessable
> information)?
>
>
>
>
> I have seen some attempts to solve this problem, such as with setting up SSL
> certs for apache's use if the certs private key is encrypted, you have to
> supply the private key decryption password at application startup and the
> key then lives in memory.
>
> This isn't very practical, in my opinion, in most environments I have seen
> because an unplanned outage could require system reboots by your
> monitoring personnel who might not know the application decryption
> passphrase and higher administrators have to be called in to start the
> services up properly.
>
> With web pages written in something like PHP, it would be even less practical
> because then you would have to design some sort of daemon that stays
> running in memory and the php code would ask the daemon to decrypt the
> database credentials for each request. Or another approach would be to
> thing like that like using the IPC capabilities of your operating system and
> using shared memory. To use this shared memory you would have some
> program that runs on system startup and you enter the credentials and they
> get saved to this shared memory location and your other apps or php pages
> can use the IPC interface to read this memory.
>
> Even these things have their issues because if the attacker can trigger a
> memory dump that gets written to disk (like causing a BSOD and you have full
> memory dumps enabled) and the attacker has local filesystem access they
> could then read the dump from disk (after the system comes back up) and
> obtain the key like that.
>
>
>
>
> I'd like to hear you all's thoughts on this so I can learn something new.
>
>
>
>
> -B

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