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F5 Networks BIG-IP : F5 SSH server key size vulnerability (K43404629)

medium Nessus Plugin ID 139824

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Synopsis

The remote device is missing a vendor-supplied security patch.

Description

The version of F5 Networks BIG-IP installed on the remote host is prior to 12.1.5.2 / 13.1.3.6 / 14.1.2.4 / 15.0.1.4 / 15.1.0.5 / 16.0.0. It is, therefore, affected by a vulnerability as referenced in the K43404629 advisory.

 The BIG-IP and BIG-IQ host OpenSSH servers use keys less than 2048 bits that are no longer considered secure.(CVE-2020-5917)ImpactThe BIG-IP system may be vulnerable to man-in-the-middle attacks and/or insecure SSH communications. Some security scanners, such as the Qualys Scanner, recognize that the OpenSSH server uses 1024-bit digital signature algorithm (DSA) keys and reports it as vulnerable (QID 38733).For adequate security, current best practices require 2048-bit and longer RSA keys. For more information, refer toNIST Special Publication 800-131A Revision 2: Transitioning the Use of Cryptographic Algorithms and Key Lengths.

Tenable has extracted the preceding description block directly from the F5 Networks BIG-IP security advisory.

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

Solution

Upgrade to one of the non-vulnerable versions listed in the F5 Solution K43404629.

See Also

https://my.f5.com/manage/s/article/K43404629

Plugin Details

Severity: Medium

ID: 139824

File Name: f5_bigip_SOL43404629.nasl

Version: 1.9

Type: local

Published: 8/26/2020

Updated: 10/8/2025

Configuration: Enable paranoid mode

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3.6

CVSS v2

Risk Factor: Medium

Base Score: 4.3

Temporal Score: 3.2

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

CVSS Score Source: CVE-2020-5917

CVSS v3

Risk Factor: Medium

Base Score: 5.9

Temporal Score: 5.2

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

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

Vulnerability Information

CPE: cpe:/a:f5:big-ip_application_security_manager, cpe:/a:f5:big-ip_access_policy_manager, cpe:/a:f5:big-ip_advanced_firewall_manager, cpe:/a:f5:big-ip_application_acceleration_manager, cpe:/a:f5:big-ip_global_traffic_manager, cpe:/a:f5:big-ip_link_controller, cpe:/a:f5:big-ip_local_traffic_manager, cpe:/a:f5:big-ip_policy_enforcement_manager, cpe:/a:f5:big-ip_domain_name_system, cpe:/h:f5:big-ip, cpe:/a:f5:big-ip_application_visibility_and_reporting

Required KB Items: Host/local_checks_enabled, Host/BIG-IP/hotfix, Host/BIG-IP/modules, Host/BIG-IP/version, Settings/ParanoidReport

Exploit Ease: No known exploits are available

Patch Publication Date: 8/25/2020

Vulnerability Publication Date: 8/26/2020

Reference Information

CVE: CVE-2020-5917

IAVA: 2020-A-0395-S