Re: Serious bug in security update for Crypt::CBC

[Kjetil Kjernsmo]

Hi all!

Sorry to be jumping in without preserving the In-Reply-To.

Allard Hoeve wrote:
I'm afraid this new package introduces some serious errors in software 
that depends on this package. I have tested the new package on three 
different Sarge machines with the following results. Please reproduce 
using attached perl script.   

This bug jumped up and bit us too during testing, and it has been 
reported as bug #356810: http://bugs.debian.org/356810
so, it is now clear that it poses a serious problem for users, as it 
breaks the default behaviour.

However,
Please remove the update from the security archive.

...it is not that simple. If you read the original advisory:
http://www.securityfocus.com/archive/1/archive/1/425966/100/0/threaded
you'll see that we have  (indirectly) been relying on weak and 
deprecated behaviour. While this is not the sort of breakage you expect 
from stable, it underlines that security is not just about blindly 
upgrading packages. 

So, it is probably better to get a heads-up from something that breaks 
down than getting the heads up from someone who breaks in... :-)

The problem in this case is that we don't know if it is serious:
  The difficulty of breaking data encrypted using this flawed algorithm
   is unknown, but it should be assumed that all information encrypted   
   in this way has been, or could someday be, compromised.

Given that the upgrade certainly breaks stable, a DSA could have 
suggested the workaround as the correct path for sysadmins:
  If using Crypt::CBC versions 2.16 and lower, pass the -salt=1 option
   to Crypt::CBC-new().
I.e., say you should do this now to upgrade your systems. 

Many users are likely to be bit by this upgrade, so, indeed, it may be a 
reasonable path to remove the security upgrade and instead suggest the 
workaround.

Best,

Kjetil
-- 
Kjetil Kjernsmo
Information Systems Developer
Opera Software ASA


pgpQXF0ABTsYf.pgp
Description: PGP signature

Serious bug in security update for Crypt::CBC

[Allard Hoeve]

Dear Martin,


From: Martin Schulze [EMAIL PROTECTED]
Reply-To: debian-security@lists.debian.org
To: Debian Security Announcements debian-security-announce@lists.debian.org
Subject: [SECURITY] [DSA 996-1] New Crypt::CBC packages fix cryptographic
weakness

For the stable distribution (sarge) this problem has been fixed in
version 2.12-1sarge1.


I'm afraid this new package introduces some serious errors in software 
that depends on this package. I have tested the new package on three 
different Sarge machines with the following results. Please reproduce 
using attached perl script.


It is the simplest of perl scripts and it functions correctly with 
libcrypt-cbc-perl version 2.12-1:



[EMAIL PROTECTED]:~$ dpkg -l libcrypt-cbc-perl | grep '^ii'
ii  libcrypt-cbc-p 2.12-1 Implementation of cipher block 
[EMAIL PROTECTED]:~$ perl crypt-decrypt.pl

allard
[EMAIL PROTECTED]:~$


After the upgrade to libcrypt-cbc-perl version 2.12-1sarge1:


[EMAIL PROTECTED]:~$ sudo apt-get install libcrypt-cbc-perl=2.12-1sarge1
[..]
[EMAIL PROTECTED]:~$ dpkg -l libcrypt-cbc-perl | grep '^ii'
ii  libcrypt-cbc-p 2.12-1sarge1   Implementation of cipher block 
[EMAIL PROTECTED]:~$ perl crypt-decrypt.pl


[EMAIL PROTECTED]:~$


Please remove the update from the security archive.

Regards,

Allard Hoeve#!/usr/bin/perl
use strict;
use warnings;
use Crypt::CBC;

my $cbc   = new Crypt::CBC({ key = abcdefghi, cipher = Blowfish });
my $encrypted = $cbc-encrypt(allard);

undef $cbc;

$cbc  = new Crypt::CBC({ key = abcdefghi, cipher = Blowfish });
my $decrypted = $cbc-decrypt($encrypted);

print $decrypted\n;