full-disclosure - Re: PuTTY private key passphrase stealing attack

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Message-ID: <4C06C421.5090307@extendedsubset.com>
Date: Wed, 02 Jun 2010 15:50:41 -0500
From: Marsh Ray <marsh@...endedsubset.com>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: PuTTY private key passphrase stealing attack

On 6/2/2010 2:58 PM, paul.szabo@...ney.edu.au wrote:
>> ... someone with access to a single account could use this to
>> gain the password for that account, and hence possibly sudo access.
> 
> Oh yes, someone with access to an account has... access to that.
> If he wanted sudo, then just have a fake sudo: one that traps the
> password and runs the real sudo after; or one that runs the real
> sudo but prepending the "bad" command.

Which is an argument against having sudo ask for the password at all:
users are expected to type in their password to any command prompt or
dialog box that asks for it.

Even when the app is legitimate, it still exposes the plaintext password
to a much greater stack of software. This is something Vista got right:
UAC is a darned secure way to type in your password (but not much else).

Once the attacker has the plaintext credentials, he can return at a
later time or take those creds to other systems. E.g. certain directory
systems effectively require the same password to be valid on every
machine in the domain/realm. Some common VPN protocols allow an attacker
who obtains the password to decrypt your captured traffic
retro-actively. This may expand the scope of the breach considerably.

IMHO password expiration policies don't help much. How does forcing
users to make new passwords every 30 days help against an attacker who
only needs the credentials for milliseconds?

- Marsh

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