Scientific Linux Security Update : openssh on SL7.x x86_64

This script is Copyright (C) 2015 Tenable Network Security, Inc.


Synopsis :

The remote Scientific Linux host is missing one or more security
updates.

Description :

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.

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.

- 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.

- 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.

- 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.

- 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.

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.

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

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

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

See also :

http://www.nessus.org/u?baf1505f

Solution :

Update the affected packages.

Risk factor :

High / CVSS Base Score : 8.5
(CVSS2#AV:N/AC:L/Au:N/C:P/I:N/A:C)

Family: Scientific Linux Local Security Checks

Nessus Plugin ID: 87567 ()

Bugtraq ID:

CVE ID: CVE-2015-5600
CVE-2015-6563
CVE-2015-6564

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