Red Hat Security Advisory: openssh security, bug fix, and enhancement update Security Advisory secalert@redhat.com Red Hat Security Response Team RHSA-2012:0884 Final 4 4 2012-06-20T08:35:00Z Current version 2012-06-20T08:35:00Z 2012-06-20T08:35:00Z Red Hat rhsa-to-cvrf 1.0.1484 2012-06-20T09:04:15Z Updated openssh packages that fix one security issue, several bugs, and add various enhancements are now available for Red Hat Enterprise Linux 6. The Red Hat Security Response Team has rated this update as having low security impact. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available from the CVE link in the References section. OpenSSH is OpenBSD's Secure Shell (SSH) protocol implementation. These packages include the core files necessary for the OpenSSH client and server. A denial of service flaw was found in the OpenSSH GSSAPI authentication implementation. A remote, authenticated user could use this flaw to make the OpenSSH server daemon (sshd) use an excessive amount of memory, leading to a denial of service. GSSAPI authentication is enabled by default ("GSSAPIAuthentication yes" in "/etc/ssh/sshd_config"). (CVE-2011-5000) These updated openssh packages also provide fixes for the following bugs: * SSH X11 forwarding failed if IPv6 was enabled and the parameter X11UseLocalhost was set to "no". Consequently, users could not set X forwarding. This update fixes sshd and ssh to correctly bind the port for the IPv6 protocol. As a result, X11 forwarding now works as expected with IPv6. (BZ#732955) * The sshd daemon was killed by the OOM killer when running a stress test. Consequently, a user could not log in. With this update, the sshd daemon sets its oom_adj value to -17. As a result, sshd is not chosen by OOM killer and users are able to log in to solve problems with memory. (BZ#744236) * If the SSH server is configured with a banner that contains a backslash character, then the client will escape it with another "\" character, so it prints double backslashes. An upstream patch has been applied to correct the problem and the SSH banner is now correctly displayed. (BZ#809619) In addition, these updated openssh packages provide the following enhancements: * Previously, SSH allowed multiple ways of authentication of which only one was required for a successful login. SSH can now be set up to require multiple ways of authentication. For example, logging in to an SSH-enabled machine requires both a passphrase and a public key to be entered. The RequiredAuthentications1 and RequiredAuthentications2 options can be configured in the /etc/ssh/sshd_config file to specify authentications that are required for a successful login. For example, to set key and password authentication for SSH version 2, type: echo "RequiredAuthentications2 publickey,password" >> /etc/ssh/sshd_config For more information on the aforementioned /etc/ssh/sshd_config options, refer to the sshd_config man page. (BZ#657378) * Previously, OpenSSH could use the Advanced Encryption Standard New Instructions (AES-NI) instruction set only with the AES Cipher-block chaining (CBC) cipher. This update adds support for Counter (CTR) mode encryption in OpenSSH so the AES-NI instruction set can now be used efficiently also with the AES CTR cipher. (BZ#756929) * Prior to this update, an unprivileged slave sshd process was run as the sshd_t context during privilege separation (privsep). sshd_t is the SELinux context used for running the sshd daemon. Given that the unprivileged slave process is run under the user's UID, it is fitting to run this process under the user's SELinux context instead of the privileged sshd_t context. With this update, the unprivileged slave process is now run as the user's context instead of the sshd_t context in accordance with the principle of privilege separation. The unprivileged process, which might be potentially more sensitive to security threats, is now run under the user's SELinux context. (BZ#798241) Users are advised to upgrade to these updated openssh packages, which contain backported patches to resolve these issues and add these enhancements. After installing this update, the OpenSSH server daemon (sshd) will be restarted automatically. Please see https://www.redhat.com/footer/terms-of-use.html Copyright © 2012 Red Hat, Inc. All rights reserved. Low https://rhn.redhat.com/errata/RHSA-2012-0884.html https://rhn.redhat.com/errata/RHSA-2012-0884.html https://access.redhat.com/security/updates/classification/#low https://access.redhat.com/security/updates/classification/#low https://bugzilla.redhat.com/show_bug.cgi?id=657378 https://bugzilla.redhat.com/show_bug.cgi?id=657378 https://bugzilla.redhat.com/show_bug.cgi?id=732955 https://bugzilla.redhat.com/show_bug.cgi?id=732955 https://bugzilla.redhat.com/show_bug.cgi?id=797384 https://bugzilla.redhat.com/show_bug.cgi?id=797384 Red Hat Enterprise Linux Desktop Optional (v. 6) Red Hat Enterprise Linux HPC Node Optional (v. 6) Red Hat Enterprise Linux Workstation Optional (v. 6) Red Hat Enterprise Linux Workstation (v. 6) Red Hat Enterprise Linux HPC Node (v. 6) Red Hat Enterprise Linux Server Optional (v. 6) Red Hat Enterprise Linux Desktop (v. 6) Red Hat Enterprise Linux Server (v. 6) openssh-5.3p1-81.el6.src.rpm openssh-5.3p1-81.el6 as a component of Red Hat Enterprise Linux Desktop Optional (v. 6) openssh-5.3p1-81.el6 as a component of Red Hat Enterprise Linux HPC Node Optional (v. 6) openssh-5.3p1-81.el6 as a component of Red Hat Enterprise Linux Workstation Optional (v. 6) openssh-5.3p1-81.el6 as a component of Red Hat Enterprise Linux Workstation (v. 6) openssh-5.3p1-81.el6 as a component of Red Hat Enterprise Linux HPC Node (v. 6) openssh-5.3p1-81.el6 as a component of Red Hat Enterprise Linux Server Optional (v. 6) openssh-5.3p1-81.el6 as a component of Red Hat Enterprise Linux Desktop (v. 6) openssh-5.3p1-81.el6 as a component of Red Hat Enterprise Linux Server (v. 6) A denial of service flaw was found in the OpenSSH GSSAPI authentication implementation. A remote, authenticated user could use this flaw to make the OpenSSH server daemon (sshd) use an excessive amount of memory, leading to a denial of service. GSSAPI authentication is enabled by default ("GSSAPIAuthentication yes" in "/etc/ssh/sshd_config"). 2011-08-01T00:00:00Z 2011-08-01T00:00:00Z CVE-2011-5000 6Client-optional:openssh-5.3p1-81.el6 6Client:openssh-5.3p1-81.el6 6ComputeNode-optional:openssh-5.3p1-81.el6 6ComputeNode:openssh-5.3p1-81.el6 6Server-optional:openssh-5.3p1-81.el6 6Server:openssh-5.3p1-81.el6 6Workstation-optional:openssh-5.3p1-81.el6 6Workstation:openssh-5.3p1-81.el6 Low 3.5 AV:N/AC:M/Au:S/C:N/I:N/A:P Before applying this update, make sure all previously-released errata relevant to your system have been applied. This update is available via the Red Hat Network. Details on how to use the Red Hat Network to apply this update are available at https://access.redhat.com/knowledge/articles/11258 https://rhn.redhat.com/errata/RHSA-2012-0884.html https://www.redhat.com/security/data/cve/CVE-2011-5000.html CVE-2011-5000 https://bugzilla.redhat.com/show_bug.cgi?id=809938 bz#809938: CVE-2011-5000 openssh: post-authentication resource exhaustion bug via GSSAPI