-----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Vulnerability in ssh-agent January 28, 1998 16:00 GMT Number I-026 ______________________________________________________________________________ PROBLEM: A vulnerability exists in the SSH cryptographic login program. PLATFORM: Unix - SSH versions 1.2.17 through 1.2.21 SSH prior to 1.2.17 are subject to a similar attack F-secure SSH prior ro 1.3.3 DAMAGE: By exploiting this vulnerability, an unauthorized person on the same host may login to a remote server as a person utilizing SSH. SOLUTION: Upgrade or apply fixes listed below ______________________________________________________________________________ VULNERABILITY You are urged to upgrade to a non-vulnerable version of SSH as ASSESSMENT: soon as possible or apply the fixes. ______________________________________________________________________________ [ Start Secure Networks Inc. ] ###### ## ## ###### ## ### ## ## ###### ## # ## ## ## ## ### ## ###### . ## ## . ######. 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 . 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 . For more information regarding this advisory, contact Secure Networks Inc. as . 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. Secure Networks [ End Secure Networks Inc. ] ______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Secure Networks Inc. for the information contained in this bulletin. ______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. 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Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. 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LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) I-016: SCO /usr/bin/X11/scoterm Vulnerability I-017: statd Buffer Overrun Vulnerability I-018: FTP Bounce Vulnerability I-019: Tools Generating IP Denial-of-Service Attacks I-020: Cisco 7xx password buffer overflow - DOS I-021: "smurf" IP Denial-of-Service Attacks I-022: IBM AIX "routed" daemon Vulnerability I-023: Macro Virus Update I-024: CGI Security Hole in EWS1.1 Vulnerability I-025: Windows NT based Web Servers File Access Vulnerability -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBNM9tp7nzJzdsy3QZAQHloQQAiV9gJaSq9ug6v28CRPIPXiceNnFPRM5f N5leaJSwE3OFYj68I7Cc8/Yw1vsK8F2i0PXs3w2hbrc3hfjStepuMKNB2iZYRiyz ggv1VCjYZKOm1rUhRjcqay4Q/JYyCb/qbUEdawD1MfackgWKAvorCzI0eEm8cJ1P jpPo33GB5bY= =7/cr -----END PGP SIGNATURE-----