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Fw: SNI-23: SSH - Vulnerability in ssh-agent
Thought you might want to see this
-----Original Message-----
From: Secure Networks Inc. <sni@SECURENETWORKS.COM>
To: BUGTRAQ@NETSPACE.ORG <BUGTRAQ@NETSPACE.ORG>
Date: Wednesday, January 21, 1998 12:44 AM
Subject: SNI-23: SSH - Vulnerability in ssh-agent
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> Secure Networks Inc.
>
> Security Advisory
> January 20, 1998
>
> Vulnerability in ssh-agent
>
>
>This advisory details a vulnerabily in the SSH cryptographic login
>program. The vulnerability enables users to use RSA credentials
>belonging to other users who use the ssh-agent program. This
>vulnerability may allow an attacker on the same local host to login
>to a remote server as the user utilizing SSH.
>
>
>Problem Description:
>~~~~~~~~~~~~~~~~~~~~
>
>In order to avoid forcing users of RSA based authentication to go
>through the trouble of retyping their pass phrase every time they wish
>to use ssh, slogin, or scp, the SSH package includes a program called
>ssh-agent, which manages RSA keys for the SSH program. The ssh-agent
>program creates a mode 700 directory in /tmp, and then creates an
>AF_UNIX socket in that directory. Later, the user runs the ssh-add
>program, which adds his private key to the set of keys managed by the
>ssh-agent program. When the user wishes to access a service which
>permits him to log in using only his RSA key, the SSH client connects
>to the AF_UNIX socket, and asks the ssh-agent program for the key.
>
>Unfortunately, when connecting to the AF_UNIX socket, the SSH client is
>running as super-user, and performs insufficient permissions checking.
>This makes it possible for users to trick their SSH clients into using
>credentials belonging to other users. The end result is that any user
>who utilizes RSA authentication AND uses ssh-agent, is vulnerable.
>Attackers can utilize this vulnerability to access remote accounts
>belonging to the ssh-agent user.
>
>
>Technical Details
>~~~~~~~~~~~~~~~~~
>
>When communicating with the ssh-agent program, the SSH program issues a
>connect() system call as super-user to access the AF_UNIX socket. By
>utilizing symbolic links, an attacker can cause the SSH program to
>connect to an alternate user's AF_UNIX socket, and read their RSA
>credentials. After the credentials have been read, SSH will use these
>credentials to logon to the remote system as the victim.
>
>
>Vulnerable Systems:
>~~~~~~~~~~~~~~~~~~~
>
>This vulnerability effects the Unix versions of SSH ONLY.
>
>SSH for unix versions 1.2.17 through 1.2.21 are vulnerable if installed
>with default permissions. Versions of SSH prior to 1.2.17 are subject to
>a similar (but different) attack.
>
>F-Secure SSH for Unix systems prior to release 1.3.3 ARE vulnerable.
>
>You can determine the version of SSH you are running by issuing the case
>sensitive command:
>
>% ssh -V
>
>Version 1.1 of the windows-based SSH client sold by Data Fellows Inc.
>under the F-Secure brand name is NOT vulnerable to this attack.
>
>Versions 1.0 and 1.0a of Mac SSH are NOT vulnerable to this attack.
>
>
>Fix Resolution:
>~~~~~~~~~~~~~~~
>
>Non-commercial users:
>
>If using the free non-commercial SSH distribution for Unix, administrators
>are urged to upgrade to SSH 1.2.22 or later. Updated versions of the free
>unix SSH can be found at ftp://ftp.cs.hut.fi/pub/ssh
>
>
>Commercial users:
>
>F-Secure SSH version 1.3.3 fixes this security problem. If you are using
>the commercial Data Fellows SSH package and you have a support contract,
>you can obtain SSH version 1.3.3 from your local retailer.
>
>Users without a support contract can obtain a diff file which fixes
>this problem. This file can be obtained from:
>
>http://www.DataFellows.com/f-secure/support/ssh/bug/su132patch.html
>
>
>Workaround:
>
>As a temporary workaround, administrators may remove the setuid bit from
>the SSH binary. This will prevent the attack from working, but will
>disable a form of authentication documented as rhosts-RSA. For example,
>if your SSH binary is in the /usr/local/bin directory, the following
>command will remove the setuid bit from the SSH binary:
>
># chmod u-s /usr/local/bin/ssh
>
>
>Additional Information
>~~~~~~~~~~~~~~~~~~~~~~
>
>SSH is a cryptographic rsh, rlogin, and rcp replacement. SSH was
>written by Tatu Ylonen <ylo@cs.hut.fi>. For more information about the
>noncommercial unix version of SSH, please see http://www.cs.hut.fi/ssh
>
>Commercial versions of ssh are marketed by Data Fellows Inc. For
>information about the F-secure ssh derivatives sold by Data Fellows Inc,
>please see http://www.DataFellows.com/f-secure
>
>This vulnerability was discovered by David Sacerdote <davids@secnet.com>.
>
>For more information regarding this advisory, contact Secure Networks
>Inc. as <sni@secnet.com>. A PGP public key is provided below if
>privacy is required.
>
>Type Bits/KeyID Date User ID
>pub 1024/9E55000D 1997/01/13 Secure Networks Inc. <sni@secnet.com>
> Secure Networks <security@secnet.com>
>
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>
>Copyright Notice
>~~~~~~~~~~~~~~~~
>The contents of this advisory are Copyright (C) 1997 Secure Networks
>Inc, and may be distributed freely provided that no fee is charged for
>distribution, and that proper credit is given.
>
> You can find Secure Networks papers at ftp://ftp.secnet.com/pub/papers
> and advisories at ftp://ftp.secnet.com/advisories
>
> You can browse our web site at http://www.secnet.com
>
> You can subscribe to our security advisory mailing list by sending mail
> to majordomo@secnet.com with the line "subscribe sni-advisories"
>
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