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7.5

Cisco ASA VPN may let attackers connect without certificate

CVE-2018-0227 · published 8 years ago
Summary

The SSL VPN client certificate check on Cisco Adaptive Security Appliance and Firepower Threat Defense software can be bypassed, allowing an unauthenticated remote user to establish a VPN connection. This could let an attacker gain network access that should have been blocked. Apply the vendor’s security update or patch as soon as possible to fix the verification logic.

What to do

The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.

Affected software
VendorProductAffected versions
cisco adaptive_security_appliance_software >= 9.4.4, <= 9.4.4.13
>= 9.5.3.7, <= 9.5.3.9
>= 9.6.2.9, <= 9.6.2.21
>= 9.6.3, <= 9.6.3.17
9.4.3.1
9.4.3.2
9.5.2.7
9.5.2.8
cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco secure_firewall_threat_defense >= 6.0, <= 6.0.1.4
>= 6.1.0, <= 6.1.0.5
cpe:2.3:a:cisco:secure_firewall_threat_defense:*:*:*:*:*:*:*:*
Original advisory text
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,...
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.
References
Fix within
Internet-facing 14 days
Internal 60 days
  • Not known to be exploited
  • Can be exploited automatically
  • Gives an attacker partial control
Severity
7.5 High
Exploitation
2% chance of attack within 30 days
Type
CWE-295Improper Certificate Validation
Timeline
Published19 Apr 2018
Updated4 Nov 2026
First seen29 Sep 2026
Sources
CVE-2018-0227 · NVD
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