oss-security - CVE Request: Debian (others?) openssh-server: Forced Command handling leaks private information to ssh clients

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Date: Thu, 26 Jan 2012 16:19:30 -0700
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security@...ts.openwall.com
Subject: CVE Request: Debian (others?) openssh-server: Forced Command handling
 leaks private information to ssh clients

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=657445

======================================================================

From: Bjoern Buerger <bbu@...gutronix.de>
To: Debian Bug Tracking System <submit@...s.debian.org>
Subject: openssh-server: Forced Command handling leaks private
information to ssh
 clients
Date: Thu, 26 Jan 2012 11:46:18 +0100

Package: openssh-server
Version: 1:5.5p1-6+squeeze1
Severity: normal


The handling of multiple forced commands in ~/.ssh/authorized key leaks
information about other configured forced commands to the user. This
affects tools lile gitolite, which makes heavy use of forced commands
(For gitolite, this bug means: A user can obtain some or all usernames
 with access to the same gitolite setup by just using the verbose
 switch of his ssh client, which is a really nasty thing).

Example:

 User "bbu" on machine "ptx" has three configured forced commands for
 keys test{1,2,3}_rsa.pub:

 command="/usr/bin/first_command" ssh-rsa [...third_key...]
 command="/usr/bin/second_command" ssh-rsa [...second_key...]
 command="/usr/bin/third_command" ssh-rsa [...third_key...]

 Now, if the user of test1_rsa.pub uses the "-v" switch of
 his ssh client, he gets just his command:

 foo@bar:~/ssh_debug$ ssh -i test1_rsa -v bbu@ptx 2>&1 | grep Forced\
command
 debug1: Remote: Forced command: /usr/bin/first_command
 debug1: Remote: Forced command: /usr/bin/first_command

 but the user of test2_rsa.pub sees two commands:

 foo@bar:~/ssh_debug$ ssh -i test2_rsa -v bbu@ptx 2>&1 | grep Forced\
command
 debug1: Remote: Forced command: /usr/bin/first_command
 debug1: Remote: Forced command: /usr/bin/second_command
 debug1: Remote: Forced command: /usr/bin/first_command
 debug1: Remote: Forced command: /usr/bin/second_command

 and for user of test3_rsa.pub:

 bbu@...ra:~/ssh_debug$ ssh -i test3_rsa -v bbu@ptx 2>&1 | grep Forced\
command
 debug1: Remote: Forced command: /usr/bin/first_command
 debug1: Remote: Forced command: /usr/bin/second_command
 debug1: Remote: Forced command: /usr/bin/third_command
 debug1: Remote: Forced command: /usr/bin/first_command
 debug1: Remote: Forced command: /usr/bin/second_command
 debug1: Remote: Forced command: /usr/bin/third_command
======================================================================

I have confirmed that this works exactly as advertised on Debian 6. I
have confirmed that RHEL/Fedora are not affected (you only get shown the
command for your specific SSH key).

So Debian is definitely affected, but I am concerned others may be as
well (is this Debian specific or does it affect all users of that
version of OpenSSH?). I suggest you test this on your own distributions
as well.






-- 
Kurt Seifried Red Hat Security Response Team (SRT)

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