openssh security update

ID CESA-2009:1287
Type centos
Reporter CentOS Project
Modified 2009-09-15T19:27:52


CentOS Errata and Security Advisory CESA-2009:1287

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 SSH protocol. An attacker able to perform a man-in-the-middle attack may be able to obtain a portion of plain text from an arbitrary ciphertext block when a CBC mode cipher was used to encrypt SSH communication. This update helps mitigate this attack: OpenSSH clients and servers now prefer CTR mode ciphers to CBC mode, and the OpenSSH server now reads SSH packets up to their full possible length when corruption is detected, rather than reporting errors early, reducing the possibility of successful plain text recovery. (CVE-2008-5161)

This update also fixes the following bug:

  • the ssh client hung when trying to close a session in which a background process still held tty file descriptors open. With this update, this so-called "hang on exit" error no longer occurs and the ssh client closes the session immediately. (BZ#454812)

In addition, this update adds the following enhancements:

  • the SFTP server can now chroot users to various directories, including a user's home directory, after log in. A new configuration option -- ChrootDirectory -- has been added to "/etc/ssh/sshd_config" for setting this up (the default is not to chroot users). Details regarding configuring this new option are in the sshd_config(5) manual page. (BZ#440240)

  • the executables which are part of the OpenSSH FIPS module which is being validated will check their integrity and report their FIPS mode status to the system log or to the terminal. (BZ#467268, BZ#492363)

All OpenSSH users are advised to upgrade to these updated 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.

Merged security bulletin from advisories:

Affected packages: openssh openssh-askpass openssh-clients openssh-server

Upstream details at: