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Category:   Application (Security)  >   OpenSSH Vendors:
OpenSSH on Debian Lets Remote Users Prevent Logins
SecurityTracker Alert ID:  1020891
SecurityTracker URL:
CVE Reference:   CVE-2008-4109   (Links to External Site)
Date:  Sep 17 2008
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 4.3, 4.6
Description:   A vulnerability was reported in OpenSSH on Debian. A remote user can cause denial of service conditions.

A remote user may be able to exploit a flaw in the signal handler (which calls a function that is not safe to be called asynchronously) to cause the ssh daemon to leave zombie processes. If enough processes are left, subsequent login attempts may be blocked.

The vulnerability can be triggered by accident.

Impact:   A remote user can prevent ssh logins.
Solution:   Debian has issued a fix (4.3p2-9etch3, 4.6p1-1).

The Debian advisory will be available at:

Vendor URL: (Links to External Site)
Cause:   State error
Underlying OS:  Linux (Debian)

Message History:   None.

 Source Message Contents

Subject:  [SECURITY] [DSA 1638-1] New openssh packages fix denial of service

Hash: SHA1

- ------------------------------------------------------------------------
Debian Security Advisory DSA-1638-1                                   Florian Weimer
September 16, 2008          
- ------------------------------------------------------------------------

Package        : openssh
Vulnerability  : remote
Problem type   : unsafe signal handler
Debian-specific: no
CVE Id(s)      : CVE-2008-4109
Debian Bug     : 498678

It has been discovered that the signal handler implementing the login
timeout in Debian's version of the OpenSSH server uses functions which
are not async-signal-safe, leading to a denial of service
vulnerability (CVE-2008-4109).

The problem was originally corrected in OpenSSH 4.4p1 (CVE-2006-5051),
but the patch backported to the version released with etch was

Systems affected by this issue suffer from lots of zombie sshd
processes.  Processes stuck with a "[net]" process title have also been
observed.  Over time, a sufficient number of processes may accumulate
such that further login attempts are impossible.  Presence of these
processes does not indicate active exploitation of this vulnerability.
It is possible to trigger this denial of service condition by accident.

For the stable distribution (etch), this problem has been fixed in
version 4.3p2-9etch3.

For the unstable distribution (sid) and the testing distribution
(lenny), this problem has been fixed in version 4.6p1-1.

We recommend that you upgrade your openssh packages.

Upgrade instructions
- --------------------

wget url
        will fetch the file for you
dpkg -i file.deb
        will install the referenced file.

If you are using the apt-get package manager, use the line for
sources.list as given below:

apt-get update
        will update the internal database
apt-get upgrade
        will install corrected packages

You may use an automated update by adding the resources from the
footer to the proper configuration.

Debian GNU/Linux 4.0 alias etch
- -------------------------------

Source archives:
    Size/MD5 checksum:   275859 d36cb34826bb92eca24a9397369baee6
    Size/MD5 checksum:   920186 239fc801443acaffd4c1f111948ee69c
    Size/MD5 checksum:     1310 1888a56e6050c8b8c2caf95e9da1db84

Architecture independent packages:
    Size/MD5 checksum:    91378 2748b67458de398e05e7c05227a0c612
    Size/MD5 checksum:     1052 f47a80d017cd3184bc981a38ced31ee8

alpha architecture (DEC Alpha)
    Size/MD5 checksum:   782932 e7f3b896603dc1aebadb370d79ab90f5
    Size/MD5 checksum:   100580 8ed4b61e252f3080073134abae2a36cd
    Size/MD5 checksum:   213712 9eb6b65f9292db607a4b2d6bf498c54f
    Size/MD5 checksum:   266512 81805fcb11c56d7252ecdf4a1e74d713
    Size/MD5 checksum:   198516 d294a1db5f4257c4c58154bb160232f1

amd64 architecture (AMD x86_64 (AMD64))
    Size/MD5 checksum:   710490 816deaa292a89d07a1d8b6ad196eb72d
    Size/MD5 checksum:    99976 05a863e6cd0aaced1cf8c774d7573274
    Size/MD5 checksum:   183846 a9c89a870bb58463606ec8b736643144
    Size/MD5 checksum:   244368 9d0b3126c34e338b4f5216284518aea8
    Size/MD5 checksum:   171380 2cf03617de7bd22ff03b85f8ca2b25f0

arm architecture (ARM)
    Size/MD5 checksum:   650726 a50736277f77d29a8cd59be5de31efe8
    Size/MD5 checksum:    99754 bee5a81d4168699a324ff572d6e436d6
    Size/MD5 checksum:   164866 067f69be0283f3bb3cf697f4312d2bbb
    Size/MD5 checksum:   218966 2a8dfbfc4e5abe2d333f20e123ad38ad
    Size/MD5 checksum:   171672 a0ce63abaee1e7cfbaf64e62dc8164b5

hppa architecture (HP PA RISC)
    Size/MD5 checksum:   732946 3177a89f68634880a3da10e054abe538
    Size/MD5 checksum:   189606 92ce0ac13874e3ec7ef20e7d97221850
    Size/MD5 checksum:   249864 191165420d41b4ea84f7ae820a61dee1
    Size/MD5 checksum:   198138 af0b7c29c951135595170b63251dd484
    Size/MD5 checksum:   100532 55db615aae32e2adf40dbe79b5fc7cf1

i386 architecture (Intel ia32)
    Size/MD5 checksum:    99766 5844bc9b9aebd6da32ceba7b80017dea
    Size/MD5 checksum:   162626 b8ce1b90a26b1097ddfc5fb8323dc1d3
    Size/MD5 checksum:   223696 087b8d33303c197953ba2a9904345592
    Size/MD5 checksum:   154038 308a4f0d415532bfa7b3836d70aaf4ea
    Size/MD5 checksum:   659992 df6bf6ae7a34e91d5677115bbdb01b73

ia64 architecture (Intel ia64)
    Size/MD5 checksum:   962182 49dc85d747e2a50d8e37b9c4e7428e6e
    Size/MD5 checksum:   269904 bf013bd6ab07afab765d6ca84be21666
    Size/MD5 checksum:   338240 3fe40ae711c9c0c3689f5d8c50b70af7
    Size/MD5 checksum:   101440 c49ecbbdd0101c8a90fcc9d4b60ae1c8
    Size/MD5 checksum:   251934 793c1d31b7a179a766ed57d6ad5649cf

mips architecture (MIPS (Big Endian))
    Size/MD5 checksum:   732114 9ec13c1de7481000339c6f10ebb7f149
    Size/MD5 checksum:   191298 d190ada9fd3c0420d949126c02fa85da
    Size/MD5 checksum:   251044 c97d6f7d9baf2b1678289e9e067ea4d4
    Size/MD5 checksum:   200554 028987ca5310b3fb2e6003ba385b2bd0
    Size/MD5 checksum:    99996 f52e7996ddb5f7bff8d6ced65f82bd2d

powerpc architecture (PowerPC)
    Size/MD5 checksum:   168340 030a27c9ce4287f28669ba4a5af8247c
    Size/MD5 checksum:   237020 3cde6fe4ab569ca83cc9616572be11ca
    Size/MD5 checksum:   173280 38bdde6d16b07399ba996dd66a6311ae
    Size/MD5 checksum:   700832 6397ec69df1deb0c5e0bc4c58ffae141
    Size/MD5 checksum:   101248 bfcd1a41ede062d9449f5be7eb7cd16f

s390 architecture (IBM S/390)
    Size/MD5 checksum:   246734 9181c374dcb69441bd7ec030aadfb911
    Size/MD5 checksum:   188516 a3786ab0a693ddb4f81fdeeead01ec51
    Size/MD5 checksum:   100226 73ec19e480b2e9b4c2809a04a77d27b9
    Size/MD5 checksum:   725828 7ff9eafecb36d2147305e08289ca22a4
    Size/MD5 checksum:   196900 23c3164ff897157de7fdd6b334a39e95

sparc architecture (Sun SPARC/UltraSPARC)
    Size/MD5 checksum:   640266 7c833bcc2eb5a606be3bc4243313bc97
    Size/MD5 checksum:   218194 eceb87ee9c789edfae071afe782c3a5f
    Size/MD5 checksum:   166716 869791f368a6de4cfc3ddd818be8c33f
    Size/MD5 checksum:    99714 8564652d41a2c1709c6d3794b241ddc5
    Size/MD5 checksum:   158356 d2f2015c554f5f1cd918d07559f82ebd

  These files will probably be moved into the stable distribution on
  its next update.

- ---------------------------------------------------------------------------------
For apt-get: deb stable/updates main
For dpkg-ftp: dists/stable/updates/main
Mailing list:
Package info: `apt-cache show <pkg>' and<pkg>
Version: GnuPG v1.4.9 (GNU/Linux)



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