#48612 Expat "billion laughs attack" vulnerability (CVE-2013-0340)

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

From: Marius Bakke <marius@gnu.org>

To: bug-guix@gnu.org

Subject: Expat "billion laughs attack" vulnerability (CVE-2013-0340)

Date: Sun, 23 May 2021 17:15:11 +0200

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Greetings Guix,

What's old is new again!  Expat 2.4.0 was recently released with a
fix for a denial of service issue dubbed "billion laughs attack":

  https://github.com/libexpat/libexpat/blob/R_2_4_0/expat/Changes
  https://en.wikipedia.org/wiki/Billion_laughs_attack

Seeing as this vulnerability appears to be eight years old and is
"merely" a DoS: is it worth fixing on the 'master' branch (and
re-grafting pretty much everything)?

In any case I've attached a patch that does just that and I'm currently
using it on my system.  I'm hesitant to push it because of the grafting
cost and would like others opinion.

[0001-gnu-expat-Replace-with-2.4.0-fixes-CVE-2013-0340.patch (text/x-patch, attachment)]

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Message #8 received at 48612@debbugs.gnu.org (full text, mbox, reply):

From: Maxime Devos <maximedevos@telenet.be>

To: Marius Bakke <marius@gnu.org>, 48612@debbugs.gnu.org

Subject: Re: bug#48612: Expat "billion laughs attack" vulnerability (CVE-2013-0340)

Date: Sun, 23 May 2021 20:40:29 +0200

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Marius Bakke schreef op zo 23-05-2021 om 17:15 [+0200]:
> Greetings Guix,
> 
> What's old is new again!  Expat 2.4.0 was recently released with a
> fix for a denial of service issue dubbed "billion laughs attack":
> 
>   https://github.com/libexpat/libexpat/blob/R_2_4_0/expat/Changes
>   https://en.wikipedia.org/wiki/Billion_laughs_attack
> 
> Seeing as this vulnerability appears to be eight years old and is
> "merely" a DoS: is it worth fixing on the 'master' branch (and
> re-grafting pretty much everything)?

Since this is ‘merely’ a DoS that does not lead to an exploit, I
would simply upgrade the package on 'core-updates'. However, I don't
run any servers. At worst, an attacker could bring down a computer or
burn CPU cyles but nothing else. Bad, but not an exploit and not worth
a graft in my opinion. If this attack is found to cause an annoyance in
the wild, we can easily add a graft later.

> 
> In any case I've attached a patch that does just that and I'm currently
> using it on my system.  I'm hesitant to push it because of the grafting
> cost and would like others opinion.
> 

I would like others opinion as well.

Greetings,
Maxime.

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Message #11 received at 48612@debbugs.gnu.org (full text, mbox, reply):

From: Leo Famulari <leo@famulari.name>

To: Marius Bakke <marius@gnu.org>

Cc: 48612@debbugs.gnu.org

Subject: Re: bug#48612: Expat "billion laughs attack" vulnerability (CVE-2013-0340)

Date: Mon, 24 May 2021 13:06:47 -0400

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On Sun, May 23, 2021 at 05:15:11PM +0200, Marius Bakke wrote:
> Greetings Guix,
> 
> What's old is new again!  Expat 2.4.0 was recently released with a
> fix for a denial of service issue dubbed "billion laughs attack":
> 
>   https://github.com/libexpat/libexpat/blob/R_2_4_0/expat/Changes
>   https://en.wikipedia.org/wiki/Billion_laughs_attack
> 
> Seeing as this vulnerability appears to be eight years old and is
> "merely" a DoS: is it worth fixing on the 'master' branch (and
> re-grafting pretty much everything)?
> 
> In any case I've attached a patch that does just that and I'm currently
> using it on my system.  I'm hesitant to push it because of the grafting
> cost and would like others opinion.

I think it's okay to graft it. The distro is big enough that there will
always be some grafted packages. However, I'd like to try ungrafting at
regular periods; based on the current ungrafting build cycle, monthly
may be reasonable.

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Message #18 received at 48612-done@debbugs.gnu.org (full text, mbox, reply):

From: Leo Famulari <leo@famulari.name>

To: Marius Bakke <marius@gnu.org>

Cc: 48612-done@debbugs.gnu.org

Subject: Re: bug#48612: Expat "billion laughs attack" vulnerability (CVE-2013-0340)

Date: Wed, 2 Jun 2021 23:16:29 -0400

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On Mon, May 24, 2021 at 01:06:47PM -0400, Leo Famulari wrote:
> I think it's okay to graft it. The distro is big enough that there will
> always be some grafted packages. However, I'd like to try ungrafting at
> regular periods; based on the current ungrafting build cycle, monthly
> may be reasonable.

I updated your patch to use expat 2.4.1 and pushed as
6d71f6a73cd27d61d3302b9658893428af6314d2

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