CentOS 7 : openssh (CESA-2015:2088)

high Nessus Plugin ID 87128


The remote CentOS host is missing one or more security updates.


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.

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.

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.


Update the affected openssh packages.

See Also


Plugin Details

Severity: High

ID: 87128

File Name: centos_RHSA-2015-2088.nasl

Version: 2.10

Type: local

Agent: unix

Published: 12/2/2015

Updated: 1/4/2021

Supported Sensors: Frictionless Assessment Agent, Frictionless Assessment AWS, Frictionless Assessment Azure

Risk Information

CVSS Score Source: CVE-2015-5600


Risk Factor: Medium

Score: 5.9


Risk Factor: High

Base Score: 8.5

Temporal Score: 6.3

Vector: AV:N/AC:L/Au:N/C:P/I:N/A:C

Temporal Vector: E:U/RL:OF/RC:C

Vulnerability Information

CPE: p-cpe:/a:centos:centos:openssh, p-cpe:/a:centos:centos:openssh-askpass, p-cpe:/a:centos:centos:openssh-clients, p-cpe:/a:centos:centos:openssh-keycat, p-cpe:/a:centos:centos:openssh-ldap, p-cpe:/a:centos:centos:openssh-server, p-cpe:/a:centos:centos:openssh-server-sysvinit, p-cpe:/a:centos:centos:pam_ssh_agent_auth, cpe:/o:centos:centos:7

Required KB Items: Host/local_checks_enabled, Host/CentOS/release, Host/CentOS/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 11/30/2015

Vulnerability Publication Date: 8/3/2015

Reference Information

CVE: CVE-2015-5600, CVE-2015-6563, CVE-2015-6564

RHSA: 2015:2088