Scientific Linux Security Update : openssh on SL6.x i386/x86_64
Medium Nessus Plugin ID 78641
SynopsisThe remote Scientific Linux host is missing one or more security updates.
DescriptionIt 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.
It was found that OpenSSH did not properly handle certain AcceptEnv parameter values with wildcard characters. A remote attacker could use this flaw to bypass intended environment variable restrictions.
This update also fixes the following bugs :
- Based on the SP800-131A information security standard, the generation of a digital signature using the Digital Signature Algorithm (DSA) with the key size of 1024 bits and RSA with the key size of less than 2048 bits is disallowed after the year 2013. After this update, ssh-keygen no longer generates keys with less than 2048 bits in FIPS mode. However, the sshd service accepts keys of size 1024 bits as well as larger keys for compatibility reasons.
- Previously, the openssh utility incorrectly set the oom_adj value to -17 for all of its children processes.
This behavior was incorrect because the children processes were supposed to have this value set to 0.
This update applies a patch to fix this bug and oom_adj is now properly set to 0 for all children processes as expected.
- Previously, if the sshd service failed to verify the checksum of an installed FIPS module using the fipscheck library, the information about this failure was only provided at the standard error output of sshd. As a consequence, the user could not notice this message and be uninformed when a system had not been properly configured for FIPS mode. To fix this bug, this behavior has been changed and sshd now sends such messages via the syslog service.
- When keys provided by the pkcs11 library were removed from the ssh agent using the 'ssh-add -e' command, the user was prompted to enter a PIN. With this update, a patch has been applied to allow the user to remove the keys provided by pkcs11 without the PIN.
In addition, this update adds the following enhancements :
- With this update, ControlPersist has been added to OpenSSH. The option in conjunction with the ControlMaster configuration directive specifies that the master connection remains open in the background after the initial client connection has been closed.
- When the sshd daemon is configured to force the internal SFTP session, and the user attempts to use a connection other than SFTP, the appropriate message is logged to the /var/log/secure file.
- Support for Elliptic Curve Cryptography modes for key exchange (ECDH) and host user keys (ECDSA) as specified by RFC5656 has been added to the openssh packages.
However, they are not enabled by default and the user has to enable them manually.
SolutionUpdate the affected packages.