[Secure-testing-team] Bug#481860: openssh-server upgrade didn't remove all compromised keys from /etc/ssh

[Vincent Lefevre]

Package: openssh-server
Version: 1:4.7p1-10
Severity: grave
Tags: security
Justification: user security hole

When I upgraded openssh-server, ssh_host_dsa_key has been replaced
because it was compromised, but not ssh_host_rsa_key, but this one
was compromised too!

$ ll /etc/ssh
-rw-r--r-- 1 root root 2064867 2008-05-13 16:23:21 blacklist.DSA-1024
-rw-r--r-- 1 root root 2064867 2008-05-17 17:03:45 blacklist.RSA-1024
-rw-r--r-- 1 root root 2064867 2008-05-13 16:23:21 blacklist.RSA-2048
-rw-r--r-- 1 root root   88039 2003-05-01 15:29:57 moduli
-rw-r--r-- 1 root root    1595 2008-01-11 01:54:42 ssh_config
-rw------- 1 root root     668 2008-05-15 11:12:51 ssh_host_dsa_key
-rw------- 1 root root     668 2008-01-30 16:20:56 ssh_host_dsa_key.broken
-rw-r--r-- 1 root root     598 2008-05-15 11:12:51 ssh_host_dsa_key.pub
-rw-r--r-- 1 root root     602 2008-01-30 16:20:56 ssh_host_dsa_key.pub.broken
-rw------- 1 root root     883 2008-01-30 16:20:56 ssh_host_rsa_key
-rw-r--r-- 1 root root     222 2008-01-30 16:20:56 ssh_host_rsa_key.pub
-rw-r--r-- 1 root root   14274 2008-01-30 16:42:08 ssh_known_hosts
-rw-r--r-- 1 root root    1881 2008-04-17 15:30:22 sshd_config
-rw-r--r-- 1 root root    1873 2008-04-17 15:17:19 sshd_config~
$ for i in /etc/ssh/ssh_host_*pub*; echo $i && ssh-vulnkey $i
/etc/ssh/ssh_host_dsa_key.pub
Not blacklisted: 1024 5f:84:36:c0:a3:4f:86:a3:0e:7b:67:5f:71:4f:46:66 root at vin
/etc/ssh/ssh_host_dsa_key.pub.broken
COMPROMISED: 1024 00:9d:b1:dd:7b:93:6d:92:92:84:1a:19:61:28:cb:6a root at butanol
/etc/ssh/ssh_host_rsa_key.pub
COMPROMISED: 1024 6b:89:cd:4a:c4:f8:c8:b1:7d:60:25:6b:2a:05:af:42 root at butanol

As you can see, the old ssh_host_dsa_key was detected as compromised,
thus renamed as ssh_host_dsa_key.broken and regenerated, but nothing
has been done on the old compromised ssh_host_rsa_key key.

So, in short, openssh-server gave incorrect information about
compromised keys. Until now, I thought that all my keys were OK
after the upgrade, but this is now clearly not the case!

-- System Information:
Debian Release: lenny/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.24.5-20080423 (SMP w/2 CPU cores; PREEMPT)
Locale: LANG=POSIX, LC_CTYPE=en_US.ISO8859-1 (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/bash

Versions of packages openssh-server depends on:
ii  adduser                3.107             add and remove users and groups
ii  debconf [debconf-2.0]  1.5.22            Debian configuration management sy
ii  dpkg                   1.14.19           package maintenance system for Deb
ii  libc6                  2.7-11            GNU C Library: Shared libraries
ii  libcomerr2             1.40.8-2          common error description library
ii  libkrb53               1.6.dfsg.3-2      MIT Kerberos runtime libraries
ii  libpam-modules         0.99.7.1-6        Pluggable Authentication Modules f
ii  libpam-runtime         0.99.7.1-6        Runtime support for the PAM librar
ii  libpam0g               0.99.7.1-6        Pluggable Authentication Modules l
ii  libselinux1            2.0.59-1          SELinux shared libraries
ii  libssl0.9.8            0.9.8g-10         SSL shared libraries
ii  libwrap0               7.6.q-15          Wietse Venema's TCP wrappers libra
ii  lsb-base               3.2-12            Linux Standard Base 3.2 init scrip
ii  openssh-blacklist      0.2               list of default blacklisted OpenSS
ii  openssh-client         1:4.7p1-10        secure shell client, an rlogin/rsh
ii  zlib1g                 1:1.2.3.3.dfsg-12 compression library - runtime

Versions of packages openssh-server recommends:
ii  xauth                         1:1.0.3-1  X authentication utility

-- debconf information:
* ssh/vulnerable_host_keys:
  ssh/new_config: true
* ssh/use_old_init_script: true
  ssh/encrypted_host_key_but_no_keygen:
  ssh/disable_cr_auth: false