CVE-2018-0277 in Identity Services Engine
Summary
by MITRE
A vulnerability in the Extensible Authentication Protocol-Transport Layer Security (EAP-TLS) certificate validation during EAP authentication for the Cisco Identity Services Engine (ISE) could allow an unauthenticated, remote attacker to cause the ISE application server to restart unexpectedly, causing a denial of service (DoS) condition on an affected system. The vulnerability is due to incomplete input validation of the client EAP-TLS certificate. An attacker could exploit this vulnerability by initiating EAP authentication over TLS to the ISE with a crafted EAP-TLS certificate. A successful exploit could allow the attacker to restart the ISE application server, resulting in a DoS condition on the affected system. The ISE application could continue to restart while the client attempts to establish the EAP authentication connection. If an attacker attempted to import the same EAP-TLS certificate to the ISE trust store, it could trigger a DoS condition on the affected system. This exploit vector would require the attacker to have valid administrator credentials. The vulnerability affects Cisco ISE, Cisco ISE Express, and Cisco ISE Virtual Appliance. Cisco Bug IDs: CSCve31857.
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Analysis
by VulDB Data Team • 03/13/2023
The vulnerability described in CVE-2018-0277 represents a critical denial of service weakness within Cisco's Identity Services Engine (ISE) platform, specifically affecting the Extensible Authentication Protocol-Transport Layer Security (EAP-TLS) implementation. This flaw exists in the certificate validation process during EAP authentication, creating an avenue for remote attackers to disrupt network access services. The vulnerability impacts multiple Cisco ISE deployments including the standard ISE, ISE Express, and ISE Virtual Appliance variants, making it particularly concerning for organizations relying on these authentication services for network security.
The technical root cause of this vulnerability stems from incomplete input validation within the EAP-TLS certificate processing mechanism of the Cisco ISE application. When the system receives a client EAP-TLS certificate during authentication, it fails to properly validate the certificate's structure and content before processing it. This incomplete validation allows maliciously crafted certificates to trigger unexpected behavior within the application server. The vulnerability manifests when an attacker initiates EAP authentication over TLS with a specially crafted certificate that exploits the validation gap, causing the ISE application server to crash and restart automatically. This behavior creates a continuous restart loop that effectively renders the authentication service unavailable to legitimate users.
The operational impact of this vulnerability extends beyond simple service disruption as it can create persistent denial of service conditions that are difficult to resolve without manual intervention. The continuous restart cycle prevents legitimate authentication attempts from completing successfully, effectively blocking network access for users attempting to connect to the protected network segments. Network administrators face the challenge of identifying the source of the disruption since the system appears to be restarting due to internal application errors rather than external network attacks. The vulnerability's exploitation requires minimal network access but can cause significant operational disruption to organizations dependent on ISE for network authentication and access control.
This vulnerability aligns with CWE-20, "Improper Input Validation," which specifically addresses situations where input validation is insufficient to prevent malicious inputs from causing unexpected behavior. The attack pattern follows techniques documented in the MITRE ATT&CK framework under T1499.004, "Endpoint Denial of Service," where attackers target application-level services to create availability disruptions. The vulnerability's requirement for valid administrator credentials to import certificates to the trust store indicates it may be exploitable through privilege escalation or credential compromise scenarios. Organizations should consider implementing network segmentation and monitoring to detect unusual restart patterns that could indicate exploitation attempts, while also ensuring proper access controls to prevent unauthorized certificate imports. The vulnerability demonstrates the importance of robust input validation in authentication systems and highlights the potential for seemingly benign certificate processing to become a critical security weakness when validation is incomplete.