SB2016080202 - Multiple vulnerabilities in OpenSSH for Ubuntu

Description

This security bulletin contains information about 5 secuirty vulnerabilities.

1) User enumeration via covert timing channel (CVE-ID: CVE-2016-6210)

The vulnerability allows a remote attacker to enumerate users on system.

The vulnerability exists in most systems where the Blowfish algorithm runs faster than SHA256/SHA512. A remote unauthenticated attacker can determine valid usernames by sending a specially crafted request with a large password (approximately 10,000 characters) to the target ssh daemon. On systems where a valid user's password has been hashed with SHA256/SHA512, the response time will be shorter for a non-existent username than for a valid username.

Successful exploitation of this vulnerability may result in disclosure or user logins.

2) Disclosure of potentially sensitive timing information (CVE-ID: N/A)

The vulnerability allows a remote attacker to obtain potentially sensitive timing information.

The vulnerability exists in OpenSSH. A remote attacker can detect timing differences in the ssh(1) and sshd(8) MAC verification for Encrypt-then-MAC (EtM) mode transport MAC algorithms.

Successful exploitation of this vulnerability may result in disclosure of system information.

3) Sensitive timing information disclosure (CVE-ID: N/A)

The vulnerability allows a remote attacker to obtain potentially sensitive timing information.

The vulnerability exists in OpenSSH. A remote attacker may be able to observe timing differences in the ssh(1) and sshd(8) CBC padding oracle countermeasures.

Successful exploitation of this vulnerability may result in disclosure of system information.

4) Consuming excessive CPU resources on the target system (CVE-ID: CVE-2016-6515)

The vulnerability allows a remote attacker to consume excessive CPU resources on the target system.

The vulnerability exists in the crypt(3) function, which accepts passwords longer that 1024 characters in auth_password() function in the auth_passwd.c . A remote unauthenticated attacker can submit a very long string as a password and consume excessive CPU resources.

Successful exploitation of this vulnerability may result in denial of service.

5) Incorrect handling of environment files (CVE-ID: CVE-2015-8325)

The vulnerability allows a local user to execute arbitrary code on the target system.

The vulnerability exists in portable version of OpenSSH. A local user can execute arbitrary code as root by setting specially crafted environment variables to conduct attacks against the 'bin/login' process on systems, where PAM is configured to read user-specified environment variables and 'sshd_config' is set to 'UseLogin=yes'.

Successful exploitation of this vulnerability may result in complete compromise of vulnerable system.

Remediation

Install update from vendor's website.

References

• http://www.openssh.com/txt/release-7.3