CVE-2019-1851 in Identity Services Engine
Summary
by MITRE
A vulnerability in the External RESTful Services (ERS) API of the Cisco Identity Services Engine (ISE) could allow an authenticated, remote attacker to generate arbitrary certificates signed by the Internal Certificate Authority (CA) Services on ISE. This vulnerability is due to an incorrect implementation of role-based access control (RBAC). An attacker could exploit this vulnerability by crafting a specific HTTP request with administrative credentials. A successful exploit could allow the attacker to generate a certificate that is signed and trusted by the ISE CA with arbitrary attributes. The attacker could use this certificate to access other networks or assets that are protected by certificate authentication.
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Analysis
by VulDB Data Team • 09/21/2023
The vulnerability identified as CVE-2019-1851 resides within the External RESTful Services API of Cisco Identity Services Engine (ISE) platforms, representing a critical security flaw that undermines the integrity of the system's certificate management infrastructure. This weakness specifically targets the Internal Certificate Authority services that operate within the ISE environment, creating a pathway for authenticated remote attackers to compromise the trust model that secures network access controls. The vulnerability stems from improper implementation of role-based access control mechanisms, which should have prevented unauthorized certificate generation activities even when administrative credentials were presented.
The technical exploitation of this vulnerability requires an attacker to craft a specific HTTP request that leverages administrative authentication credentials to bypass the intended access controls within the ERS API. This flaw manifests as a direct violation of the principle of least privilege, where the RBAC implementation fails to properly validate the scope of administrative capabilities associated with the authenticated session. The attacker can manipulate the API to generate certificates that appear to be legitimately signed by the ISE's internal CA, effectively creating a trusted certificate authority within the network infrastructure that the attacker controls. This misimplementation allows for arbitrary certificate attributes to be set, potentially enabling the creation of certificates with elevated privileges or access rights that would normally be restricted.
The operational impact of this vulnerability extends beyond simple certificate generation, as it fundamentally compromises the certificate-based authentication system that many network environments rely upon for access control. When an attacker successfully generates a trusted certificate, they can leverage it to gain access to other network segments, services, or assets that require certificate authentication for authorization. This creates a persistent backdoor within the network infrastructure that can be used to maintain access, move laterally between systems, or establish unauthorized communication channels. The vulnerability essentially allows attackers to impersonate legitimate network entities and bypass security controls that depend on certificate validation for access decisions.
Organizations affected by this vulnerability should implement immediate mitigations including disabling the ERS API when not actively required, implementing additional access controls through network segmentation, and monitoring for unauthorized certificate generation activities. The vulnerability aligns with CWE-285, which addresses improper authorization issues in access control mechanisms, and maps to ATT&CK techniques related to privilege escalation and credential access through certificate manipulation. Cisco has released patches and updates to address this vulnerability, and organizations should ensure all ISE deployments are updated to versions that contain proper RBAC enforcement within the ERS API. Network administrators should also consider implementing certificate monitoring solutions that can detect anomalous certificate generation patterns and alert on potentially malicious certificate issuance activities.