OpenSSH < 7.3 Multiple Vulnerabilities

This script is Copyright (C) 2016 Tenable Network Security, Inc.


Synopsis :

The SSH server running on the remote host is affected by multiple
vulnerabilities.

Description :

According to its banner, the version of OpenSSH running on the remote
host is prior to 7.3. It is, therefore, affected by multiple
vulnerabilities :

- A flaw exists that is due to the program returning
shorter response times for authentication requests with
overly long passwords for invalid users than for valid
users. This may allow a remote attacker to conduct a
timing attack and enumerate valid usernames.
(CVE-2016-6210)

- A denial of service vulnerability exists in the
auth_password() function in auth-passwd.c due to a
failure to limit password lengths for password
authentication. An unauthenticated, remote attacker can
exploit this, via a long string, to consume excessive
CPU resources, resulting in a denial of service
condition. (CVE-2016-6515)

- An unspecified flaw exists in the CBC padding oracle
countermeasures that allows an unauthenticated, remote
attacker to conduct a timing attack. (VulnDB 142343)

- A flaw exists due to improper operation ordering of MAC
verification for Encrypt-then-MAC (EtM) mode transport
MAC algorithms when verifying the MAC before decrypting
any ciphertext. An unauthenticated, remote attacker can
exploit this, via a timing attack, to disclose sensitive
information. (VulnDB 142344)

Note that Nessus has not tested for these issues but has instead
relied only on the application's self-reported version number.

See also :

http://www.openssh.com/txt/release-7.3
https://marc.info/?l=openbsd-announce&m=147005433429403

Solution :

Upgrade to OpenSSH version 7.3 or later.

Risk factor :

High / CVSS Base Score : 7.8
(CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:C)
CVSS Temporal Score : 6.4
(CVSS2#E:F/RL:OF/RC:ND)
Public Exploit Available : true

Family: Misc.

Nessus Plugin ID: 93194 ()

Bugtraq ID: 92212

CVE ID: CVE-2016-6515
CVE-2016-6210

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