OpenSSH MaxAuthTries Bypass

High Nessus Plugin ID 86122

New! Vulnerability Priority Rating (VPR)

Tenable calculates a dynamic VPR for every vulnerability. VPR combines vulnerability information with threat intelligence and machine learning algorithms to predict which vulnerabilities are most likely to be exploited in attacks. Read more about what VPR is and how it's different from CVSS.

VPR Score: 4.2


The SSH server running on the remote host is affected by a security bypass vulnerability that allows password brute-force attacks.


The remote SSH server is affected by a security bypass vulnerability due to a flaw in the keyboard-interactive authentication mechanisms.
The kbdint_next_device() function in auth2-chall.c improperly restricts the processing of keyboard-interactive devices within a single connection. A remote attacker can exploit this, via a crafted keyboard-interactive 'devices' string, to bypass the normal restriction of 6 login attempts (MaxAuthTries), resulting in the ability to conduct a brute-force attack or cause a denial of service condition.


Upgrade to OpenSSH 7.0 or later.

Alternatively, this vulnerability can be mitigated on some Linux distributions by disabling the keyboard-interactive authentication method. This can be done on Red Hat Linux by setting 'ChallengeResponseAuthentication' to 'no' in the /etc/ssh/sshd_config configuration file and restarting the sshd service.

See Also

Plugin Details

Severity: High

ID: 86122

File Name: openssh_maxauthtries_bruteforce.nasl

Version: 1.9

Type: remote

Family: Misc.

Published: 2015/09/24

Updated: 2020/06/12

Dependencies: 10267

Risk Information

Risk Factor: High

VPR Score: 4.2

CVSS v2.0

Base Score: 8.5

Temporal Score: 6.3

Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:N/A:C

Temporal Vector: CVSS2#E:U/RL:OF/RC:C

CVSS v3.0

Base Score: 8.2

Temporal Score: 7.1

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/a:openbsd:openssh

Excluded KB Items: global_settings/supplied_logins_only

Exploit Available: false

Exploit Ease: No known exploits are available

Patch Publication Date: 2015/08/11

Vulnerability Publication Date: 2015/07/16

Reference Information

CVE: CVE-2015-5600

BID: 75990