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CVE Record

CVE-2018-0227: A vulnerability in the Secure Sockets Layer (SSL) Virtual Private Network (VPN) Client Certificate Authenti...

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2018-0227 is a Cisco ASA/FTD SSL VPN certificate-checking flaw. A remote unauthenticated attacker could establish an SSL VPN connection when certificate validation should reject them. For leaders, this matters because exposed VPN gateways are high-value entry points into internal networks.

Executive priority

Treat this as a high-priority VPN access-control issue. If affected SSL VPN gateways are exposed, remediation should be scheduled urgently because successful exploitation could allow unauthorized VPN connectivity before normal network defenses see internal activity.

Technical view

The issue is incorrect SSL client certificate verification in Cisco ASA SSL VPN Client Certificate Authentication. Sources say an attacker could connect without a proper private key and certificate pair, bypassing certain certificate verification steps. Cisco identifies bug CSCvg40155 and affected ASA/FTD software on listed Cisco security platforms.

Likely exposure

Exposure is most likely on Cisco ASA or FTD deployments using SSL VPN client certificate authentication, especially internet-facing VPN gateways. The bundle names ASA, ASAv, ASA 5500/5500-X, ISA 3000, ASA Services Module, Firepower 4110, and Firepower 9300 ASA modules.

Exploitation context

The source bundle does not show CISA KEV listing or cite active exploitation. The described attack is remote and unauthenticated, but no exploit maturity, observed campaigns, or public exploit details are provided here.

Researcher notes

CWE-295 fits the reported certificate validation failure. Evidence is strong for the vulnerability class and affected Cisco product families, but this bundle lacks CVSS details, fixed release data, and exploitation evidence. Avoid assuming impact beyond establishing an SSL VPN connection.

Mitigation direction

  • Check Cisco advisory cisco-sa-20180418-asa1 for affected and fixed software guidance.
  • Upgrade affected ASA or FTD software according to Cisco guidance.
  • Prioritize internet-facing SSL VPN gateways using client certificate authentication.
  • Review ICS-CERT guidance for operational environments using affected Cisco appliances.

Validation and detection

  • Inventory Cisco ASA and FTD appliances matching the affected product families.
  • Confirm whether SSL VPN client certificate authentication is enabled.
  • Compare running software versions against Cisco advisory guidance.
  • Review VPN authentication logs for unexpected successful SSL VPN certificate-authenticated sessions.
  • Document whether each exposed VPN gateway is patched, mitigated, or not affected.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CWE-295: Exact CWE lookup

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cve · low confidence lookup

CVE-2018-0227 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/aCisco Adaptive Security ApplianceCisco Adaptive Security ApplianceListed
Weakness

CWE details

CWE-295

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-295 · source CWE mapping

Improper Certificate Validation

Improper Certificate Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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