bash: Related to CVE-2016-7543: Privilege escalation possible to other user than root

Debian Bug report logs - #841856
bash: Related to CVE-2016-7543: Privilege escalation possible to other user than root

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: Ola Lundqvist <ola@inguza.com>

To: Debian Bug Tracking System <submit@bugs.debian.org>

Subject: Upstream correction of CVE-2016-7543 is incomplete

Date: Sun, 23 Oct 2016 23:10:51 +0200

[Message part 1 (text/plain, inline)]

Package: bash
Version: 4.2+dfsg-0.1+deb7u3
Tags: security, patch
Severity: important

Hi

While fixing CVE-2016-7543 for wheezy I found that the upstream correction
was incomplete. It do in fact solve the problem described in the CVE but a
very closely related problem is not solved.

The problem described in the CVE is that it is possible to privilege
escalate to root.
However the patch only fix that specific problem, not escalation change to
any other user.

The attached patch solve that problem too.

Best regards

// Ola

-- 
 --- Inguza Technology AB --- MSc in Information Technology ----
/  ola@inguza.com                    Folkebogatan 26            \
|  opal@debian.org                   654 68 KARLSTAD            |
|  http://inguza.com/                Mobile: +46 (0)70-332 1551 |
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 ---------------------------------------------------------------

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[bash43-048-backported-CVE-2016-7543-20161023.patch (text/x-patch, attachment)]

Message #10 received at 841856@bugs.debian.org (full text, mbox, reply):

From: Salvatore Bonaccorso <carnil@debian.org>

To: Ola Lundqvist <ola@inguza.com>, 841856@bugs.debian.org

Subject: Re: Bug#841856: Upstream correction of CVE-2016-7543 is incomplete

Date: Mon, 24 Oct 2016 07:00:15 +0200

[Message part 1 (text/plain, inline)]

Control: found -1 4.2+dfsg-0.1
Control: tags -1 + upstream

Hi

Adding the testcases from Ola, which were referenced at

https://lists.debian.org/debian-lts/2016/10/msg00141.html

Ola, have you reported this to upstream?

Regards,
Salvatore

[exploit.tar.gz (application/gzip, attachment)]

Message #19 received at 841856@bugs.debian.org (full text, mbox, reply):

From: Ola Lundqvist <ola@inguza.com>

To: Salvatore Bonaccorso <carnil@debian.org>

Cc: 841856@bugs.debian.org

Subject: Re: Bug#841856: Upstream correction of CVE-2016-7543 is incomplete

Date: Mon, 24 Oct 2016 08:50:46 +0200

[Message part 1 (text/plain, inline)]

Hi

No. If you want I can do that.

Please note that the patch I attached essentally disable the whole PS4
variable support so upstream can probably do something more intelligent.

/ Ola

Sent from a phone

Den 24 okt 2016 07:00 skrev "Salvatore Bonaccorso" <carnil@debian.org>:

Control: found -1 4.2+dfsg-0.1
Control: tags -1 + upstream

Hi

Adding the testcases from Ola, which were referenced at

https://lists.debian.org/debian-lts/2016/10/msg00141.html

Ola, have you reported this to upstream?

Regards,
Salvatore

[Message part 2 (text/html, inline)]

Message #24 received at 841856@bugs.debian.org (full text, mbox, reply):

From: Salvatore Bonaccorso <carnil@debian.org>

To: Ola Lundqvist <ola@inguza.com>

Cc: 841856@bugs.debian.org

Subject: Re: Bug#841856: Upstream correction of CVE-2016-7543 is incomplete

Date: Mon, 24 Oct 2016 09:08:28 +0200

Hi Ola,

Thanks for quick followup!

On Mon, Oct 24, 2016 at 08:50:46AM +0200, Ola Lundqvist wrote:
> Hi
> 
> No. If you want I can do that.

I think that would be good, to get Chet's attention on the issue. Once
it's clear, we might need to as well request a CVE for it on
oss-security.


> Please note that the patch I attached essentally disable the whole PS4
> variable support so upstream can probably do something more intelligent.

Yep, and thus I really think we should have Chet Ramey with his
upstream hat look into it.

Thanks for your work and regards,
Salvatore

Message #29 received at 841856@bugs.debian.org (full text, mbox, reply):

From: Ola Lundqvist <ola@inguza.com>

To: bug-bash@gnu.org

Cc: 841856@bugs.debian.org, Salvatore Bonaccorso <carnil@debian.org>

Subject: Correction of CVE-2016-7543 is incomplete

Date: Mon, 24 Oct 2016 10:09:10 +0200

[Message part 1 (text/plain, inline)]

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

Hi

In CVE-2016-7543 a problem was reported that it is possible to privilege
escalate to root.
The correction as seen here
http://lists.gnu.org/archive/html/bug-bash/2016-10/msg00009.html
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:
http://bugs.debian.org/841856

I have attached a tar file with exploit code. The exploit code is used like
this:
make
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

-- 
 --- Inguza Technology AB --- MSc in Information Technology ----
/  ola@inguza.com                    Folkebogatan 26            \
|  opal@debian.org                   654 68 KARLSTAD            |
|  http://inguza.com/                Mobile: +46 (0)70-332 1551 |
\  gpg/f.p.: 7090 A92B 18FE 7994 0C36 4FE4 18A1 B1CF 0FE5 3DD9  /
 ---------------------------------------------------------------

[Message part 2 (text/html, inline)]

[exploit.tar.gz (application/x-gzip, attachment)]

[CVE-2016-7543-bug-841856-20161023.patch (application/octet-stream, attachment)]

Message #34 received at 841856@bugs.debian.org (full text, mbox, reply):

From: Ola Lundqvist <ola@inguza.com>

To: Salvatore Bonaccorso <carnil@debian.org>

Cc: Ola Lundqvist <ola@inguza.com>, 841856@bugs.debian.org

Subject: Re: Bug#841856: Upstream correction of CVE-2016-7543 is incomplete

Date: Mon, 24 Oct 2016 10:09:50 +0200

[Message part 1 (text/plain, inline)]

Hi

Thanks for fast response. I have now reported it upstream as you can see in
the mail I just sent.

Best regards

// Ola

On 24 October 2016 at 09:08, Salvatore Bonaccorso <carnil@debian.org> wrote:

> Hi Ola,
>
> Thanks for quick followup!
>
> On Mon, Oct 24, 2016 at 08:50:46AM +0200, Ola Lundqvist wrote:
> > Hi
> >
> > No. If you want I can do that.
>
> I think that would be good, to get Chet's attention on the issue. Once
> it's clear, we might need to as well request a CVE for it on
> oss-security.
>
>
> > Please note that the patch I attached essentally disable the whole PS4
> > variable support so upstream can probably do something more intelligent.
>
> Yep, and thus I really think we should have Chet Ramey with his
> upstream hat look into it.
>
> Thanks for your work and regards,
> Salvatore
>



-- 
 --- Inguza Technology AB --- MSc in Information Technology ----
/  ola@inguza.com                    Folkebogatan 26            \
|  opal@debian.org                   654 68 KARLSTAD            |
|  http://inguza.com/                Mobile: +46 (0)70-332 1551 |
\  gpg/f.p.: 7090 A92B 18FE 7994 0C36 4FE4 18A1 B1CF 0FE5 3DD9  /
 ---------------------------------------------------------------

[Message part 2 (text/html, inline)]

Message #39 received at 841856@bugs.debian.org (full text, mbox, reply):

From: up201407890@alunos.dcc.fc.up.pt

To: "Ola Lundqvist" <ola@inguza.com>

Cc: bug-bash@gnu.org, 841856@bugs.debian.org, "Salvatore Bonaccorso" <carnil@debian.org>

Subject: Re: Correction of CVE-2016-7543 is incomplete

Date: Mon, 24 Oct 2016 18:37:57 +0200

Quoting "Ola Lundqvist" <ola@inguza.com>:

This is known.

I "complained" at the time, as it can be seen here:
https://lists.gnu.org/archive/html/bug-bash/2015-12/msg00112.html


> Version: all (see note below)
> Hardware: all
> Operating system: Debian GNU Linux (but all should be affected)
> Compiler: gcc
>
> Hi
>
> In CVE-2016-7543 a problem was reported that it is possible to privilege
> escalate to root.
> The correction as seen here
> http://lists.gnu.org/archive/html/bug-bash/2016-10/msg00009.html
> 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:
> http://bugs.debian.org/841856
>
> I have attached a tar file with exploit code. The exploit code is used like
> this:
> make
> 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
>
> --
>  --- Inguza Technology AB --- MSc in Information Technology ----
> /  ola@inguza.com                    Folkebogatan 26            \
> |  opal@debian.org                   654 68 KARLSTAD            |
> |  http://inguza.com/                Mobile: +46 (0)70-332 1551 |
> \  gpg/f.p.: 7090 A92B 18FE 7994 0C36 4FE4 18A1 B1CF 0FE5 3DD9  /
>  ---------------------------------------------------------------
>



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Message #44 received at 841856@bugs.debian.org (full text, mbox, reply):

From: Ola Lundqvist <ola@inguza.com>

To: up201407890@alunos.dcc.fc.up.pt

Cc: Ola Lundqvist <ola@inguza.com>, bug-bash@gnu.org, 841856@bugs.debian.org, Salvatore Bonaccorso <carnil@debian.org>

Subject: Re: Correction of CVE-2016-7543 is incomplete

Date: Mon, 24 Oct 2016 21:58:03 +0200

[Message part 1 (text/plain, inline)]

Hi

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, <up201407890@alunos.dcc.fc.up.pt> wrote:

> Quoting "Ola Lundqvist" <ola@inguza.com>:
>
> This is known.
>
> I "complained" at the time, as it can be seen here:
> https://lists.gnu.org/archive/html/bug-bash/2015-12/msg00112.html
>
>
>
> Version: all (see note below)
>> Hardware: all
>> Operating system: Debian GNU Linux (but all should be affected)
>> Compiler: gcc
>>
>> Hi
>>
>> In CVE-2016-7543 a problem was reported that it is possible to privilege
>> escalate to root.
>> The correction as seen here
>> http://lists.gnu.org/archive/html/bug-bash/2016-10/msg00009.html
>> 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:
>> http://bugs.debian.org/841856
>>
>> I have attached a tar file with exploit code. The exploit code is used
>> like
>> this:
>> make
>> 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
>>
>> --
>>  --- Inguza Technology AB --- MSc in Information Technology ----
>> /  ola@inguza.com                    Folkebogatan 26            \
>> |  opal@debian.org                   654 68 KARLSTAD            |
>> |  http://inguza.com/                Mobile: +46 (0)70-332 1551 |
>> \  gpg/f.p.: 7090 A92B 18FE 7994 0C36 4FE4 18A1 B1CF 0FE5 3DD9  /
>>  ---------------------------------------------------------------
>>
>>
>
>
> ----------------------------------------------------------------
> This message was sent using IMP, the Internet Messaging Program.
>
>


-- 
 --- Inguza Technology AB --- MSc in Information Technology ----
/  ola@inguza.com                    Folkebogatan 26            \
|  opal@debian.org                   654 68 KARLSTAD            |
|  http://inguza.com/                Mobile: +46 (0)70-332 1551 |
\  gpg/f.p.: 7090 A92B 18FE 7994 0C36 4FE4 18A1 B1CF 0FE5 3DD9  /
 ---------------------------------------------------------------

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