CVE-2018-0227: A vulnerability in the Secure Sockets Layer (SSL) Virtual Private Network (VPN) Client Certificate Authentication feature for Cisco Adaptive Security ...

Description

A vulnerability in the Secure Sockets Layer (SSL) Virtual Private Network (VPN) Client Certificate Authentication feature for Cisco Adaptive Security Appliance (ASA) could allow an unauthenticated, remote attacker to establish an SSL VPN connection and bypass certain SSL certificate verification steps. The vulnerability is due to incorrect verification of the SSL Client Certificate. An attacker could exploit this vulnerability by connecting to the ASA VPN without a proper private key and certificate pair. A successful exploit could allow the attacker to establish an SSL VPN connection to the ASA when the connection should have been rejected. This vulnerability affects Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) Software that is running on the following Cisco products: 3000 Series Industrial Security Appliances (ISA), ASA 5500 Series Adaptive Security Appliances, ASA 5500-X Series Next-Generation Firewalls, ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers, Adaptive Security Virtual Appliances (ASAv), Firepower 4110 Security Appliances, Firepower 9300 ASA Security Modules. Cisco Bug IDs: CSCvg40155.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability

2.05%

78.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Cisco	Adaptive Security Appliance Software	>= 9.4.4, <= 9.4.4.13
Cisco	Adaptive Security Appliance Software	>= 9.5.3.7, <= 9.5.3.9
Cisco	Adaptive Security Appliance Software	>= 9.6.2.9, <= 9.6.2.21
Cisco	Adaptive Security Appliance Software	>= 9.6.3, <= 9.6.3.17
Cisco	Adaptive Security Appliance Software	9.4.3.1
Cisco	Adaptive Security Appliance Software	9.4.3.2
Cisco	Adaptive Security Appliance Software	9.5.2.7
Cisco	Adaptive Security Appliance Software	9.5.2.8
Cisco	Firepower Threat Defense	>= 6.0, <= 6.0.1.4
Cisco	Firepower Threat Defense	>= 6.1.0, <= 6.1.0.5

References

http://www.securityfocus.com/bid/104018Third Party Advisory, VDB Entry
http://www.securitytracker.com/id/1040723Third Party Advisory, VDB Entry
https://ics-cert.us-cert.gov/advisories/ICSA-18-184-01Third Party Advisory, US Government Resource
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180418-asa1Vendor Advisory
http://www.securityfocus.com/bid/104018Third Party Advisory, VDB Entry
http://www.securitytracker.com/id/1040723Third Party Advisory, VDB Entry
https://ics-cert.us-cert.gov/advisories/ICSA-18-184-01Third Party Advisory, US Government Resource
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180418-asa1Vendor Advisory

Timeline

Published: Apr 19, 2018
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2018-0227?

A vulnerability in the Secure Sockets Layer (SSL) Virtual Private Network (VPN) Client Certificate Authentication feature for Cisco Adaptive Security Appliance (ASA) could allow an unauthenticated, remote attacker to establish an SSL VPN connection and bypass certain SSL certificate verification steps. The vulnerability is due to incorrect verification of the SSL Client Certificate. An attacker could exploit this vulnerability by connecting to the ASA VPN without a proper private key and certificate pair. A successful exploit could allow the attacker to establish an SSL VPN connection to the ASA when the connection should have been rejected. This vulnerability affects Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) Software that is running on the following Cisco products: 3000 Series Industrial Security Appliances (ISA), ASA 5500 Series Adaptive Security Appliances, ASA 5500-X Series Next-Generation Firewalls, ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers, Adaptive Security Virtual Appliances (ASAv), Firepower 4110 Security Appliances, Firepower 9300 ASA Security Modules. Cisco Bug IDs: CSCvg40155.

How severe is CVE-2018-0227?

CVE-2018-0227 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 2.05% probability of exploitation in the next 30 days.

How do I fix CVE-2018-0227?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.