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Date: Mon, 18 Feb 2013 19:42:32 -0800
From: Jeremi Gosney <>
Subject: Re: [PHC] Any "large verifiers" on the panel?

On 2/18/2013 3:35 PM, Solar Designer wrote:
> On Sun, Feb 17, 2013 at 09:04:33PM -0800, Jeremi Gosney wrote:
>> On 2/17/2013 8:24 PM, Daniel Franke wrote:
>>> If the attacker can obtain a shell under the same uid as the webapp
>>> process and go undetected for a while, then he can ptrace the webapp and
>>> see the passwords as they're being passed into the hashing function.
>> It does not work this way anymore. At least not on modern Linux
>> distributions that enable the Yama LSM, which I'm pretty sure all
>> distributers started doing ~ 3 years back.
> This is wishful thinking.  I'm only aware of Ubuntu doing it.
> Alexander

Hum, so it is. I knew Ubuntu started using it back in 10.10, but I could
have sworn it was pulled into the mainline kernel as well. Looking
through LKML, it appears it was only in James Morris' security preview
for 2.6.36 and was later removed.

But after further digging, it looks like OpenSUSE and SLES have also
adopted Yama. And Fedora has a new SELinux policy named
SELinuxDenyPtrace which is enabled by default, which is likely to
eventually be in RHEL as well. And of course grsecurity also has had
this functionality for quite a while (Yama is based off of spender's
work iirc), and it's very common to find grsecurity-patched kernels on
shared hosting providers. Openwall also has some variant of this
functionality as well, doesn't it?

Anyway, this all kind of detracts from my original point, which is
simply that the most common vulnerabilities that lead to password dumps
have a very high potential of yeilding an unprivileged shell,
pesudo-shell, or some other method of read-only access to portions of
the filesystem. And even without the ability to escalate privileges or
do any other kind of advanced post-exploitation, these basic
vulnerabilities alone still have the very real potential to compromise
any server secrets. As was already stated by Peter Gutmann, we can't
defend against things like ptrace anyway with the PHS. But what we can
do is ensure the integrity of the PHS is not dependent upon any kind of
server secrets, such as an encryption key. That's the important thing to
take away from this thread.

Best regards,

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