RHSA-2015:0425 - Security Advisory

Topic

Updated openssh packages that fix two security issues, several bugs, and
add various enhancements are now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having Moderate security
impact. Common Vulnerability Scoring System (CVSS) base scores, which give
detailed severity ratings, are available for each vulnerability from the
CVE links in the References section.

Description

OpenSSH is OpenBSD's SSH (Secure Shell) protocol implementation. These packages
include the core files necessary for both the OpenSSH client and server.

It was discovered that OpenSSH clients did not correctly verify DNS SSHFP
records. A malicious server could use this flaw to force a connecting client to
skip the DNS SSHFP record check and require the user to perform manual host
verification of the DNS SSHFP record. (CVE-2014-2653)

It was found that when OpenSSH was used in a Kerberos environment, remote
authenticated users were allowed to log in as a different user if they were
listed in the ~/.k5users file of that user, potentially bypassing intended
authentication restrictions. (CVE-2014-9278)

The openssh packages have been upgraded to upstream version 6.6.1, which
provides a number of bug fixes and enhancements over the previous version.
(BZ#1059667)

Bug fixes:

• An existing /dev/log socket is needed when logging using the syslog utility,

which is not possible for all chroot environments based on the user's home
directories. As a consequence, the sftp commands were not logged in the chroot
setup without /dev/log in the internal sftp subsystem. With this update, openssh
has been enhanced to detect whether /dev/log exists. If /dev/log does not exist,
processes in the chroot environment use their master processes for logging.
(BZ#1083482)

• The buffer size for a host name was limited to 64 bytes. As a consequence,

when a host name was 64 bytes long or longer, the ssh-keygen utility failed. The
buffer size has been increased to fix this bug, and ssh-keygen no longer fails
in the described situation. (BZ#1097665)

• Non-ASCII characters have been replaced by their octal representations in

banner messages in order to prevent terminal re-programming attacks.
Consequently, banners containing UTF-8 strings were not correctly displayed in a
client. With this update, banner messages are processed according to RFC 3454,
control characters have been removed, and banners containing UTF-8 strings are
now displayed correctly. (BZ#1104662)

• Red Hat Enterprise Linux uses persistent Kerberos credential caches, which are

shared between sessions. Previously, the GSSAPICleanupCredentials option was set
to "yes" by default. Consequently, removing a Kerberos cache on logout could
remove unrelated credentials of other sessions, which could make the system
unusable. To fix this bug, GSSAPICleanupCredentials is set by default to "no".
(BZ#1134447)

• Access permissions for the /etc/ssh/moduli file were set to 0600, which was

unnecessarily strict. With this update, the permissions for /etc/ssh/moduli have
been changed to 0644 to make the access to the file easier. (BZ#1134448)

• Due to the KRB5CCNAME variable being truncated, the Kerberos ticket cache was

not found after login using a Kerberos-enabled SSH connection. The underlying
source code has been modified to fix this bug, and Kerberos authentication works
as expected in the described situation. (BZ#1161173)

Enhancements:

• When the sshd daemon is configured to force the internal SFTP session, a

connection other then SFTP is used, the appropriate message is logged to the
/var/log/secure file. (BZ#1130198)

• The sshd-keygen service was run using the

"ExecStartPre=-/usr/sbin/sshd-keygen" option in the sshd.service unit file. With
this update, the separate sshd-keygen.service unit file has been added, and
sshd.service has been adjusted to require sshd-keygen.service. (BZ#1134997)

Users of openssh are advised to upgrade to these updated packages, which correct
these issues and add these enhancements.

Solution

Before applying this update, make sure all previously released errata
relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258

Affected Products

• Red Hat Enterprise Linux Server 7 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 7.7 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 7.6 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 7.5 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 7.4 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 7.3 x86_64
• Red Hat Enterprise Linux Server - AUS 7.7 x86_64
• Red Hat Enterprise Linux Server - AUS 7.4 x86_64
• Red Hat Enterprise Linux Workstation 7 x86_64
• Red Hat Enterprise Linux Desktop 7 x86_64
• Red Hat Enterprise Linux for IBM z Systems 7 s390x
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 7.7 s390x
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 7.6 s390x
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 7.5 s390x
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 7.4 s390x
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 7.3 s390x
• Red Hat Enterprise Linux for Power, big endian 7 ppc64
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 7.7 ppc64
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 7.6 ppc64
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 7.5 ppc64
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 7.4 ppc64
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 7.3 ppc64
• Red Hat Enterprise Linux for Scientific Computing 7 x86_64
• Red Hat Enterprise Linux Server from RHUI 7 x86_64
• Red Hat Enterprise Linux EUS Compute Node 7.7 x86_64
• Red Hat Enterprise Linux EUS Compute Node 7.6 x86_64
• Red Hat Enterprise Linux EUS Compute Node 7.5 x86_64
• Red Hat Enterprise Linux EUS Compute Node 7.4 x86_64
• Red Hat Enterprise Linux EUS Compute Node 7.3 x86_64
• Red Hat Enterprise Linux Server - AUS 7.6 x86_64
• Red Hat Enterprise Linux Server - AUS 7.3 x86_64
• Red Hat Enterprise Linux Server - TUS 7.7 x86_64
• Red Hat Enterprise Linux Server - TUS 7.6 x86_64
• Red Hat Enterprise Linux Server - TUS 7.3 x86_64
• Red Hat Enterprise Linux Server - Update Services for SAP Solutions 7.7 x86_64
• Red Hat Enterprise Linux Server - Update Services for SAP Solutions 7.6 x86_64
• Red Hat Enterprise Linux Server - Update Services for SAP Solutions 7.4 x86_64
• Red Hat Enterprise Linux Server - Update Services for SAP Solutions 7.3 x86_64

Fixes

• BZ - 912792 - ssh client showing Connection closed by UNKNOWN after timeout at password prompt
• BZ - 1071967 - Inconsistent error message when generating keys in FIPS mode
• BZ - 1081338 - CVE-2014-2653 openssh: failure to check DNS SSHFP records in certain scenarios
• BZ - 1084079 - sftp / symlink does not create relative links
• BZ - 1097665 - ssh-keygen with error : gethostname: File name too long
• BZ - 1102288 - AuthorizedKeysCommand does not work under the Match section
• BZ - 1134997 - sshd.service shouldn't call /usr/sbin/sshd-keygen directly using ExecStartPre
• BZ - 1143867 - sshd fails to start in FIPS mode due to ED25519 key generation
• BZ - 1153011 - sshd requires that .k5login exists even if krb5_kuserok() returns TRUE
• BZ - 1155626 - KerberosUseKuserok default changed from "yes" to "no"
• BZ - 1161173 - sshd sets KRB5CCNAME environment variable with a truncated value
• BZ - 1162620 - fatal: monitor_read: unsupported request: 82 on server while attempting GSSAPI key exchange
• BZ - 1169843 - CVE-2014-9278 openssh: ~/.k5users unexpectedly grants remote login

CVEs

• CVE-2014-2653
• CVE-2014-9278

References

• https://access.redhat.com/security/updates/classification/#moderate