-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Dear Secure Shell Community, A potential remote root exploit has been discovered in SSH Secure Shell 3.0.0, for Unix only, concerning accounts with password fields consisting of two or fewer characters. Unauthorized users could potentially log in to these accounts using any password, including an empty password. This affects SSH Secure Shell 3.0.0 for Unix only. This is a problem with password authentication to the sshd2 daemon. The SSH Secure Shell client binaries (located by default in /usr/local/bin) are not affected. SSH Secure Shell 3.0.1 fixes this problem. Please note that if using a form of authentication other than password, AND password authentication is disabled, you are NOT VULNERABLE to this issue. PLATFORMS IMPACTED: Red Hat Linux 6.1 thru 7.1 Solaris 2.6 thru 2.8 HP-UX 10.20 HP-UX 11.00 Caldera Linux 2.4 Suse Linux 6.4 thru 7.0 Please note that other platforms not listed here may also be vulnerable. PLATFORMS NOT IMPACTED: Tru64 4.0.G, NetBSD, and OpenBSD are not vulnerable. Please note that other platforms not listed here may also be immune. SCOPE Some stock machines which have default locked accounts running SSH Secure Shell 3.0 are vulnerable to arbitrary logins. This is a serious problem with Solaris, for example, which uses the sequence "NP" to indicate locked administrative accounts such as "lp", "adm", "bin" etc. Some Linux machines which have accounts with !! in the etc/passwd or /etc/shadow such as xfs or gdm are also vulnerable. Since it is relatively easy to become root after gaining access to certain accounts, we consider this a potential root exploit. DETAILED DESCRIPTION During password authentication, if the field containing the encrypted password in /etc/shadow, /etc/password, etc. is two or less characters long, SSH 3.0.0 will allow anyone to access that account with ANY password. The bug is in the code that compares the result of calling crypt(pw, salt) with the value of the encrypted password in the /etc/shadow (or /etc/password) file. SSH Secure Shell Server 3.0.0 does a bounded string compare bounded to the length of the value stored in aforementioned file (2 characters in this case) against the return value of crypt(). The return value of crypt() is 13 characters, with the first two characters being the salt value itself. The salt value used is the first two characters of the encrypted password in /etc/shadow (or /etc/password). A 2 character string comparison between the 2 character encrypted password in /etc/shadow, and the 13 character crypt() return value, whose first two characters ARE the 2 characters from the password in /etc/shadow. The strings match, and the 3.0.0 daemon then accepts the password, no matter what is input. SOLUTIONS Preferred Immediately upgrade to SSH Secure Shell 3.0.1 which will be available on our e-commerce site http://commerce.ssh.com shortly, and is available on the ftp site now - ftp://ftp.ssh.com/pub/ssh A patch for 3.0.0 source code is also available there. Alternative work-arounds Disable password authentication to the SSH Secure Shell daemon (sshd2) in the /etc/ssh2/sshd2_config and use another form of authentication such as public key, SecurID, Kerberos, certificates, Smart Cards, or hostbased to authenticate your users. These alternative authentication methods are NOT VULNERABLE. Please see our SSH Secure Shell support web pages for more information on how to enable these authentication methods. OR If you cannot disable password authentication fully, limit access to the sshd2 daemon to allow only users with entries in the /etc/passwd and /etc/shadow which exceed two characters. This can be done using the AllowUsers, AllowGroups, DenyUsers, and DenyGroups keywords in the /etc/ssh2/sshd2_config file. See our SSH Secure Shell support web pages http://www.ssh.com/support/ssh and man sshd2_config for more information. OR Assign a valid password for each account. Because it is possible that assigning a password to some system accounts could cause problems on some operating systems, this work-around is limited and is provided only as a last-resort alternative. OR Use the following patch in the source code: """ File /lib/sshsession/sshunixuser.c Function ssh_user_validate_local_password Location near line 953, before /*Authentication is accepted if the encrypted passwords are identical. */ Add lines if (strlen(correct_passwd) < 13) return FALSE; "" We apologize for any inconvenience this may cause. SSH Communications Security takes security issues very seriously, and a CERT advisory and submission to Bugtraq regarding this issue have been submitted. Please make every effort to ensure that your systems are protected using one of the above methods as quickly as possible. As this information becomes widely known, your systems could be at even greater risk if appropriate measures are not taken. SSH is fully committed to serving and supporting our users and products. While we may not be able to address each request for information on this issue individually, we will make publicly available any relevant information possible which addresses your questions and concerns. CREDITS This vulnerability was found and reported by an anonymous system administrator at the Helsinki University of Technology and by Andrew Newman of Yale University. -----BEGIN PGP SIGNATURE----- Version: PGP 7.0.1 iQA/AwUBO1jNq9BQTPJLnwPSEQKmMQCeIOd7B30wubtA3p3hrAK61dZhn08AoIx+ kAzWH6o/mdL81W9TC4tJINgp =2BQq -----END PGP SIGNATURE-----
This archive was generated by hypermail 2b30 : Fri Jul 20 2001 - 17:47:11 PDT