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Re: Correction of CVE-2016-7543 is incomplete

From: Ola Lundqvist
Subject: Re: Correction of CVE-2016-7543 is incomplete
Date: Mon, 24 Oct 2016 21:58:03 +0200


Thank you for the information. Good to know that I'm not the only one that have seen this problem.

One can of course argue that the attack vector is a little odd. That is a setuid binary making system. I thought system was safe enough, but now I have learnt otherwise.

Anyway I do not think disabling PS4 variable would hurt much. Or do anyone see that it is useful to set to something else than +?
Maybe we can allow PS4 to be expanded to some extent, but not allow it to be expanded to execute commands?

// Ola

On 24 October 2016 at 18:37, <address@hidden> wrote:
Quoting "Ola Lundqvist" <address@hidden>:

This is known.

I "complained" at the time, as it can be seen here:

Version: all (see note below)
Hardware: all
Operating system: Debian GNU Linux (but all should be affected)
Compiler: gcc


In CVE-2016-7543 a problem was reported that it is possible to privilege
escalate to root.
The correction as seen here
is not complete. Well it do prevent privilege escalation to root, but it is
possible to escalate to any other user and that may be bad too.

The problem has also been reported (by me) in Debian as you can see here:

I have attached a tar file with exploit code. The exploit code is used like
sudo make root
make test

Test 1 is the exploit for CVE-2016-7543
Test 2 is the exploit for this problem
Test 3 is just a reference test.

The proposed patch essentially disable the whole PS4 variable support for
all users (not only root as the patch was for CVE-2016-7543. Please let me
know if you have a better idea on how to handle this.

Version note: The attached correction is made on a 4.2 system with a patch
for CVE-2016-7543.
However it should apply on 4.4 as well.

Let me know if you need any further details.

Best regards

// Ola

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