CVE-2026-20211 in Identity Services Engine
Summary
by MITRE • 09/17/2026
A vulnerability in Cisco ISE could allow an authenticated, remote attacker to execute arbitrary commands on the underlying operating system of an affected device. To exploit this vulnerability, the attacker must have valid high-privileged administrative credentials.
This vulnerability is due to insecure deserialization of Java objects by the affected software. An attacker could exploit this vulnerability by sending a crafted serialized Java object to an affected device. A successful exploit could allow the attacker to obtain user-level access to the underlying operating system and then elevate privileges to root. In single-node deployments, successful exploitation of this vulnerability could cause the affected ISE node to become unavailable, resulting in a DoS condition. In that condition, endpoints that have not already authenticated would be unable to access the network until the node is restored.
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Analysis
by VulDB Data Team • 09/17/2026
The identified security flaw resides within Cisco Identity Services Engine and represents a critical risk due to its potential for remote code execution with elevated privileges. This vulnerability stems from an insecure deserialization mechanism inherent in how the software processes Java objects received over the network. Insecure deserialization is a well-documented class of vulnerabilities where untrusted data is used by an application to invoke arbitrary methods, often leading to complete system compromise. The specific technical flaw allows an attacker who has already obtained valid high-privileged administrative credentials for Cisco ISE to send a specially crafted serialized Java object to the affected device. This action triggers the insecure deserialization process within the underlying operating environment of the appliance or virtual machine hosting the service.
The operational impact of this vulnerability is severe, as it enables an authenticated attacker to execute arbitrary commands on the host operating system with root-level privileges. The exploitation path begins with obtaining user-level access through the flawed deserialization logic, which then facilitates privilege escalation to gain full control over the underlying OS. This level of access allows the adversary to manipulate system configurations, exfiltrate sensitive data, install persistent backdoors, or pivot further into the network infrastructure protected by ISE. The requirement for high-privileged administrative credentials means that this vulnerability is primarily a threat from insider threats or attackers who have already compromised an administrator account through other vectors such as phishing, credential stuffing, or lateral movement within the organization.
In single-node deployments of Cisco Identity Services Engine, successful exploitation can also result in a denial-of-service condition. Because ISE handles critical authentication and authorization functions for network endpoints, rendering the node unavailable disrupts these services entirely. Endpoints that have not yet authenticated to the network will be unable to gain access until the compromised or crashed node is restored. This availability impact underscores the importance of high-availability architectures in production environments where a single point of failure can lead to significant operational downtime and security gaps during the recovery period.
From a classification perspective, this vulnerability aligns with CWE-502, which describes Deserialization of Untrusted Data. It also maps closely to MITRE ATT&CK techniques related to Command and Scripting Interpreter execution via system APIs or indirect command invocation through Java deserialization chains. The attack vector is classified as remote but requires authentication, placing it in the category of authenticated attacks that leverage existing trust relationships within the administrative domain.
Mitigation strategies must focus on both technical controls and procedural safeguards. Immediate remediation involves applying the vendor-provided software updates that patch the insecure deserialization flaw. Organizations should ensure that all Cisco ISE nodes are updated to a version where this vulnerability is resolved. Additionally, network segmentation policies should be reviewed to restrict administrative access interfaces to only those IP addresses or subnets from which legitimate administrators connect. Implementing strict input validation and avoiding the use of Java serialization for untrusted data in future development cycles can prevent similar issues. Security teams should also monitor for anomalous administrative login attempts and unusual outbound connections originating from ISE nodes, as these may indicate exploitation activity. Regular audits of privileged account usage and enforcement of multi-factor authentication for administrative access further reduce the risk of an attacker obtaining the necessary credentials to exploit this flaw.