8.5 - RHSA-2015:2088

Problem Description:

Updated openssh packages that fix multiple 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.

2. Relevant releases/architectures:

Red Hat Enterprise Linux Client (v. 7) - x86_64 Red Hat Enterprise Linux Client Optional (v. 7) - x86_64 Red Hat Enterprise Linux ComputeNode (v. 7) - x86_64 Red Hat Enterprise Linux ComputeNode Optional (v. 7) - x86_64 Red Hat Enterprise Linux Server (v. 7) - aarch64, ppc64, ppc64le, s390x, x86_64 Red Hat Enterprise Linux Server Optional (v. 7) - aarch64, ppc64, ppc64le, s390x, x86_64 Red Hat Enterprise Linux Workstation (v. 7) - x86_64 Red Hat Enterprise Linux Workstation Optional (v. 7) - x86_64

3. Description:

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

A flaw was found in the way OpenSSH handled PAM authentication when using privilege separation. An attacker with valid credentials on the system and able to fully compromise a non-privileged pre-authentication process using a different flaw could use this flaw to authenticate as other users. (CVE-2015-6563)

A use-after-free flaw was found in OpenSSH. An attacker able to fully compromise a non-privileged pre-authentication process using a different flaw could possibly cause sshd to crash or execute arbitrary code with root privileges. (CVE-2015-6564)

It was discovered that the OpenSSH sshd daemon did not check the list of keyboard-interactive authentication methods for duplicates. A remote attacker could use this flaw to bypass the MaxAuthTries limit, making it easier to perform password guessing attacks. (CVE-2015-5600)

It was found that the OpenSSH ssh-agent, a program to hold private keys used for public key authentication, was vulnerable to password guessing attacks. An attacker able to connect to the agent could use this flaw to conduct a brute-force attack to unlock keys in the ssh-agent. (BZ#1238238)

This update fixes the following bugs:

* Previously, the sshd_config(5) man page was misleading and could thus confuse the user. This update improves the man page text to clearly describe the AllowGroups feature. (BZ#1150007)

* The limit for the function for restricting the number of files listed using the wildcard character (*) that prevents the Denial of Service (DoS) for both server and client was previously set too low. Consequently, the user reaching the limit was prevented from listing a directory with a large number of files over Secure File Transfer Protocol (SFTP). This update increases the aforementioned limit, thus fixing this bug. (BZ#1160377)

* When the ForceCommand option with a pseudoterminal was used and the MaxSession option was set to "2", multiplexed SSH connections did not work as expected. After the user attempted to open a second multiplexed connection, the attempt failed if the first connection was still open. This update modifies OpenSSH to issue only one audit message per session, and the user is thus able to open two multiplexed connections in this situation. (BZ#1199112)

* The ssh-copy-id utility failed if the account on the remote server did not use an sh-like shell. Remote commands have been modified to run in an sh-like shell, and ssh-copy-id now works also with non-sh-like shells. (BZ#1201758)

* Due to a race condition between auditing messages and answers when using ControlMaster multiplexing, one session in the shared connection randomly and unexpectedly exited the connection. This update fixes the race condition in the auditing code, and multiplexing connections now work as expected even with a number of sessions created at once. (BZ#1240613)

In addition, this update adds the following enhancements:

* As not all Lightweight Directory Access Protocol (LDAP) servers possess a default schema, as expected by the ssh-ldap-helper program, this update provides the user with an ability to adjust the LDAP query to get public keys from servers with a different schema, while the default functionality stays untouched. (BZ#1201753)

* With this enhancement update, the administrator is able to set permissions for files uploaded using Secure File Transfer Protocol (SFTP). (BZ#1197989)

* This update provides the LDAP schema in LDAP Data Interchange Format (LDIF) format as a complement to the old schema previously accepted by OpenLDAP. (BZ#1184938)

* With this update, the user can selectively disable the Generic Security Services API (GSSAPI) key exchange algorithms as any normal key exchange. (BZ#1253062)

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

4. 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

5. Bugs fixed (https://bugzilla.redhat.com/):

1125110 - pam_namespace usage is not consistent across system-wide PAM configuration 1160377 - sftp is failing using wildcards and many files 1178116 - Default selinux policy prevents ssh-ldap-helper from connecting to LDAP server 1181591 - No Documentation= line in the sshd.service file 1184938 - Provide LDIF version of LPK schema 1187597 - sshd -T does not show all (default) options, inconsistency 1197666 - ssh client using HostbasedAuthentication aborts in FIPS mode 1197989 - RFE: option to let openssh/sftp force the exact permissions on newly uploaded files 1238238 - openssh: weakness of agent locking (ssh-add -x) to password guessing 1245969 - CVE-2015-5600 openssh: MaxAuthTries limit bypass via duplicates in KbdInteractiveDevices 1252844 - CVE-2015-6563 openssh: Privilege separation weakness related to PAM support 1252852 - CVE-2015-6564 openssh: Use-after-free bug related to PAM support