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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. Common Vulnerability Scoring System (CVSS) base scores, which give detailed severity ratings, are available for each vulnerability from the CVE link(s) associated with each description below.
OpenSSH is OpenBSD's Secure Shell (SSH) protocol implementation. These packages include the core files necessary for the OpenSSH client and server.
- The default OpenSSH configuration made it easy for remote attackers to exhaust unauthorized connection slots and prevent other users from being able to log in to a system. This flaw has been addressed by enabling random early connection drops by setting MaxStartups to 10:30:100 by default. For more information, refer to the sshd_config(5) man page.
- 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. Previously, to fix this, a patch was applied to keep the syslog file descriptor open. However, the syslog library was changed and the used heuristic stopped working. As a consequence, the sftp commands were not logged in the chroot setup in the internal sftp subsystem. The patch has been adjusted to the new conditions and the sftp commands are logged in the chroot setup in the internal sftp subsystem.
- Previously, when the user attempted to use their own unprotected private key, the ssh utility displayed the following message:
It is recommended that your private key files are NOT accessible by others.The key was subsequently rejected, which could have led to confusion as the behavior was inconsistent with the message. With this update, the message has been changed to:
It is required that your private key files are NOT accessible by others.
- The ssh-agent utility was unable to open more connections and could become unresponsive due to a race condition. The race condition has been fixed and ssh-agent no longer hangs in this scenario.
- If the "bindpw" option contained double quotes, it was not correctly parsed by the ssh-ldap-helper parser, and ssh-ldap-helper failed to bind to an LDAP server. With this update, ssh-ldap-helper parses the LDAP configuration files correctly.
- Prior to this update, non-ASCII characters have been replaced by their octal representations in banner messages in order to prevent terminal re-programming attacks.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.
- Previously, if the /tmp/ directory of the target user was polyinstantiated, no credentials cache was found on the remote machine after the Pluggable Authentication Module (PAM) session was initiated. As a consequence, Kerberos ticket forwarding did not work. With this update, the cache is re-created in a new /tmp/ directory after the PAM session is initiated, and Kerberos ticket forwarding now works as expected.
- Previously, if the sshd daemon was configured to force the internal SFTP session, the daemon was unable to properly handle requests for an interactive session. Consequently, sshd did not terminate SSH connections and SSH clients could became unresponsive. With this update, sshd has been modified to return an error message that the service allows SFTP connections only, and the SSH clients no longer hang in this scenario.
- This update adds support for certificate authentication of users and hosts using a new OpenSSH certificate format. Certificates contain a public key, identity information, and validity constraints, and are signed with a standard SSH public key using the ssh-keygen utility. Note that the version of ssh-keygen shipped with Red Hat Enterprise Linux 6 uses the "-Z" option for specifying the principals. For more information on this functionality, refer to the /usr/share/doc/openssh-5.3p1/PROTOCOL.certkeys file.
- This update adds support for PKCS#11 tokens. Now, OpenSSH clients are able to use smart cards for authentication.
- The KexAlgorithms configuration option has been added to client and server configuration in both the ssh utility and the sshd daemon. Specifying KexAlgorithms enables the user and the administrator to select key exchange methods and their order or preference.
- This update adds support for the SHA-2 Secure Hash Algorithm in the Hash-based Message Authentication Code (HMAC) to OpenSSH.
- The new Federal Information Processing Standard (FIPS) validation requires the random number generator (RNG) seed to have at least 112 bits of entropy instead of previous 80 bits. Therefore, the minimum value of the SSH_USE_STRONG_RNG environment variable has been increased to 14.
- The new Federal Information Processing Standard (FIPS) validation requires the Power On Self Test (POST) to run in all cases when the FIPS module is installed. With this update, the POST self test is run on the SSH client and the SSH server if the dracut-fips package has been installed.
All openssh users are advised to upgrade to these updated packages, which contain backported patches to correct these issues and add these enhancements.