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Ubuntu: OpenSSH vulnerability Print E-mail
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Posted by Benjamin D. Thomas   
Ubuntu A weakness has been discovered in the random number generator used by OpenSSL on Debian and Ubuntu systems. As a result of this weakness, certain encryption keys are much more common than they should be, such that an attacker could guess the key through a brute-force attack given minimal knowledge of the system. This particularly affects the use of encryption keys in OpenSSH.
Ubuntu Security Notice USN-612-2               May 13, 2008
openssh vulnerability

A weakness has been discovered in the random number generator used
by OpenSSL on Debian and Ubuntu systems.  As a result of this
weakness, certain encryption keys are much more common than they
should be, such that an attacker could guess the key through a
brute-force attack given minimal knowledge of the system.  This
particularly affects the use of encryption keys in OpenSSH.

This vulnerability only affects operating systems which (like
Ubuntu) are based on Debian.  However, other systems can be
indirectly affected if weak keys are imported into them.

We consider this an extremely serious vulnerability, and urge all
users to act immediately to secure their systems.

The following Ubuntu releases are affected:

Ubuntu 7.04
Ubuntu 7.10
Ubuntu 8.04 LTS

This advisory also applies to the corresponding versions of
Kubuntu, Edubuntu, and Xubuntu.

Updating your system:

1. Install the security updates

   Ubuntu 7.04:
     openssh-client                  1:4.3p2-8ubuntu1.3
     openssh-server                  1:4.3p2-8ubuntu1.3

   Ubuntu 7.10:
     openssh-client                  1:4.6p1-5ubuntu0.3
     openssh-server                  1:4.6p1-5ubuntu0.3

   Ubuntu 8.04 LTS:
     openssh-client                  1:4.7p1-8ubuntu1.1
     openssh-server                  1:4.7p1-8ubuntu1.1

   Once the update is applied, weak user keys will be automatically
   rejected where possible (though they cannot be detected in all
   cases). If you are using such keys for user authentication,
   they will immediately stop working and will need to be replaced
   (see step 3).

   OpenSSH host keys can be automatically regenerated when the
   OpenSSH security update is applied. The update will prompt for
   confirmation before taking this step.

2. Update OpenSSH known_hosts files

   The regeneration of host keys will cause a warning to be displayed
   when connecting to the system using SSH until the host key is
   updated in the known_hosts file. The warning will look like this:

   Someone could be eavesdropping on you right now (man-in-the-middle
   attack)! It is also possible that the RSA host key has just been

   In this case, the host key has simply been changed, and you
   should update the relevant known_hosts file as indicated in the
   error message.

3. Check all OpenSSH user keys

   The safest course of action is to regenerate all OpenSSH user
   keys, except where it can be established to a high degree of
   certainty that the key was generated on an unaffected system.

   Check whether your key is affected by running the ssh-vulnkey
   tool, included in the security update. By default, ssh-vulnkey
   will check the standard location for user keys (~/.ssh/id_rsa,
   ~/.ssh/id_dsa and ~/.ssh/identity), your authorized_keys file
   (~/.ssh/authorized_keys and ~/.ssh/authorized_keys2), and the
   system's host keys (/etc/ssh/ssh_host_dsa_key and

   To check all your own keys, assuming they are in the standard
   locations (~/.ssh/id_rsa, ~/.ssh/id_dsa, or ~/.ssh/identity):

   $ ssh-vulnkey

   To check all keys on your system:

   $ sudo ssh-vulnkey -a

   To check a key in a non-standard location:

   $ ssh-vulnkey /path/to/key

   If ssh-vulnkey says "Unknown (no blacklist information)",
   then it has no information about whether that key is affected.
   If in doubt, destroy the key and generate a new one.

4. Regenerate any affected user keys

   OpenSSH keys used for user authentication must be manually
   regenerated, including those which may have since been
   transferred to a different system after being generated.

   New keys can be generated using ssh-keygen, e.g.:

   $ ssh-keygen
   Generating public/private rsa key pair.
   Enter file in which to save the key (/home/user/.ssh/id_rsa):
   Enter passphrase (empty for no passphrase):
   Enter same passphrase again:
   Your identification has been saved in /home/user/.ssh/id_rsa.
   Your public key has been saved in /home/user/.ssh/
   The key fingerprint is:
   00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00 user@host

5. Update authorized_keys files (if necessary)

   Once the user keys have been regenerated, the relevant public
   keys must be propagated to any authorized_keys files on
   remote systems.  Be sure to delete the affected key.

Updated packages for Ubuntu 7.04:

  Source archives:
      Size/MD5:   275518 a8b32463625d995f31710932955f155e
      Size/MD5:     1074 2ba8f9d6823e429a87a16d1069b8bcb0
      Size/MD5:   920186 239fc801443acaffd4c1f111948ee69c

  Architecture independent packages:
      Size/MD5:     1086 ec4e33a5b72165a213aba1dc5c6e1e48
      Size/MD5:    93414 1273931c48c521f82a32c83d3c2c7f30

  amd64 architecture (Athlon64, Opteron, EM64T Xeon):
      Size/MD5:   173116 a63a1aad1a6d703701353b1a2f3aa3f1
      Size/MD5:   739306 6ebf534da00e63d36ff8d25d133c5f87
      Size/MD5:   185954 165979d39473eed093bd332294611892
      Size/MD5:   255690 5f273f1e6da9f6f572da970e7ba1680a
      Size/MD5:   101788 18268a8507e35a673ba0b88d7c8f905b

  i386 architecture (x86 compatible Intel/AMD):
      Size/MD5:   156814 338d87e0ed113fabb31bf8985c41044d
      Size/MD5:   701434 47f4f9e32772a27f390b7bf598ca692c
      Size/MD5:   165480 bb943025f0bfb39c0f080aa0c6a90507
      Size/MD5:   238154 cc0df0b6336c02dda018dd381e096150
      Size/MD5:   101494 d84b4274b86d65878b41e33db957cbec

  powerpc architecture (Apple Macintosh G3/G4/G5):
      Size/MD5:   178908 fb39252bf076dca363b34058f6c6280a
      Size/MD5:   767364 cbe597ba0193d39d115a432404471939
      Size/MD5:   184132 ebc03fba90aa40ba7e86c2bd90b4b43b
      Size/MD5:   259734 1feeb20163fb303b41a85bbd9775abe5
      Size/MD5:   104262 f781bfd69b35508129c0ce71eb0cf395

  sparc architecture (Sun SPARC/UltraSPARC):
      Size/MD5:   164240 2796884a4e9c6a0c4d228e3a2d829df4
      Size/MD5:   751366 43659331cc6f294e7657d96311db221a
      Size/MD5:   172576 f3bebc7681083a2a7dd4a91fd1ee5237
      Size/MD5:   263460 913bae4437faf91b7c4b95257ca9fe46
      Size/MD5:   101742 cf3e2aa66bfe30c2981a28063d7fa639

Updated packages for Ubuntu 7.10:

  Source archives:
      Size/MD5:   195240 fe9c399991e5e754a0837760ff9d4100
      Size/MD5:     1169 fc9b6d0a04345973f1b88ca9aa8e6a32
      Size/MD5:   946439 cee58cd226138191561fa2d484e18f49

  Architecture independent packages:
      Size/MD5:     1092 56a70a7d56d8d7722f33d60b6cd17a71
      Size/MD5:    80578 9d3e66bfbbac576c23ee4bf9827ed545

  amd64 architecture (Athlon64, Opteron, EM64T Xeon):
      Size/MD5:   176410 3167e74074387dc17c98c38e1b98fd3c
      Size/MD5:   746302 cc544fd8322a83dab8eb5f342eaca137
      Size/MD5:   193380 7defa55f2553fd71e391d33f392acd0e
      Size/MD5:   268750 6d5c5179be8f291956b30cc36d4ee091
      Size/MD5:    88726 97c9adfa3a82f9ed54286f68b41ef966

  i386 architecture (x86 compatible Intel/AMD):
      Size/MD5:   158796 e4d1cc24210b4a3327cafd41a559cd6b
      Size/MD5:   705630 c18488f740b38d1a57aef8806924de8a
      Size/MD5:   171690 af3ba10602d74429b54e256fbc982187
      Size/MD5:   249760 ab084428f73b76c5b4db1e648a222aa4
      Size/MD5:    88384 b051562fb7973c1dd92e6a8bb6b22854

  lpia architecture (Low Power Intel Architecture):
      Size/MD5:   158876 1bffbee3eed3146e3feaa2c802537699
      Size/MD5:   676546 d22322abdfa831ea95bf42540aafecd6
      Size/MD5:   171284 e59f9929f2fcc857d44131d76500c210
      Size/MD5:   243102 8b5d5ff193b90fff85cec8aee1b8cfbc
      Size/MD5:    88414 52ed9be1d8933742c15c14f7cfee11dd

  powerpc architecture (Apple Macintosh G3/G4/G5):
      Size/MD5:   180856 20b436d113f09e07b9c53301f87a551a
      Size/MD5:   773758 b7c0f8ac855ea770bbdf58284f25546e
      Size/MD5:   190236 23961af7588d4a886d818248c8c7fa15
      Size/MD5:   271988 e8bdf4fa9838997c0bd62446c59b38dd
      Size/MD5:    91094 b8756a6901f7a0337c36c7cc76d4991c

  sparc architecture (Sun SPARC/UltraSPARC):
      Size/MD5:   166884 139dc1f86d43517a46ec3915b61125e1
      Size/MD5:   758584 5b8cba657c6e53342e119d26dc9b7c61
      Size/MD5:   179096 0bccc7c29ed50a559b02e52087ae4ed2
      Size/MD5:   276534 4a4ce6ed933a3c03f632e1b3a7f34e18
      Size/MD5:    88696 a0158a6b98ff0531c1893caf4b01ebdf

Updated packages for Ubuntu 8.04 LTS:

  Source archives:
      Size/MD5:   208492 b33a4acef918d79a2d0450011fd9db88
      Size/MD5:     1135 19ea91251f9de2f6dfa6d936a8e4025b
      Size/MD5:  1009361 bea83d2e0f9ac7b3d4393d693e68b5c1

  Architecture independent packages:
      Size/MD5:     1084 ec75a470768ccd89eb6c107244d25843
      Size/MD5:    88740 16ff461b87a6baa09ececbc9697af6ed

  amd64 architecture (Athlon64, Opteron, EM64T Xeon):
      Size/MD5:   179266 1e32b7dbecf022791c6ab251a8d86117
      Size/MD5:   760430 1e6d3bdf27d9657c9eefeee0b5b6dd6f
      Size/MD5:   195488 267a48a1b35ab7855894e7785224dc57
      Size/MD5:   272820 81b2527ce22794c0281484fdc1de86c1
      Size/MD5:    96646 14c612c40c4c414eccf11db95e404a67

  i386 architecture (x86 compatible Intel/AMD):
      Size/MD5:   161826 a1081ddbc0d082133770cd8412774b01
      Size/MD5:   720024 3bcf4ba3a85f4464e13bb7d0b1574548
      Size/MD5:   174336 77153868defe66100d1ab2d4949aed80
      Size/MD5:   254010 3ad390fe06cf32b5aced76ce944839ce
      Size/MD5:    96282 505e7cd7b1b5e8f9e8c2401e61b84f78

  lpia architecture (Low Power Intel Architecture):
      Size/MD5:   161638 f14258648dc6485d895621c360caf87a
      Size/MD5:   713374 176cceb970938c3d4e664c9ecdcafe8f
      Size/MD5:   174208 12e49f067940cc99cdd91037e415d57f
      Size/MD5:   252862 4ff6983dfc76b1d9893c3eeac0da19b9
      Size/MD5:    96290 19ba2f10620c2565b41306d5392d86b9

  powerpc architecture (Apple Macintosh G3/G4/G5):
      Size/MD5:   185708 46e102bc1076e9b1efe01430e0424a14
      Size/MD5:   797090 4dc43223deedb0d4115a09d06cf352c3
      Size/MD5:   194522 d7384655c312fcba85cd31efe4b4e0de
      Size/MD5:   279012 afc9f70d7df19d39ce61b7ee18e7040a
      Size/MD5:    99064 f593634bf8755c8ef348457cd9478be9

  sparc architecture (Sun SPARC/UltraSPARC):
      Size/MD5:   169976 450612c9a43ddf84d2dd97e2422a3b22
      Size/MD5:   723070 f51ac3477b3a6554277ebb26ef6c2496
      Size/MD5:   181564 55312d8015761b003ca8abf6c6c0e6b5
      Size/MD5:   258334 c67396a961ca1baf4adb3dc60974fe8e
      Size/MD5:    96500 2ee312a10a8ff807ce94f8ecf0587588

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