CVE-2026-20306: Cisco ISE REST API RCE Vulnerability

CVE-2026-20306 Overview

CVE-2026-20306 is a command injection vulnerability in the REST API of Cisco Identity Services Engine (ISE) and Cisco ISE Passive Identity Connector (ISE-PIC). An authenticated remote attacker with valid administrative credentials can inject operating system commands through the web-based management interface. Successful exploitation results in arbitrary code execution and privilege escalation to root on the underlying operating system. The flaw carries a CVSS score of 9.1 and maps to CWE-78: Improper Neutralization of Special Elements used in an OS Command.

Critical Impact
Attackers can execute arbitrary code as root and, in single-node deployments, trigger a denial-of-service condition that blocks unauthenticated endpoints from network access.

Affected Products

Cisco Identity Services Engine (ISE)
Cisco Identity Services Engine Passive Identity Connector (ISE-PIC)
Refer to the Cisco Security Advisory for fixed release information

Discovery Timeline

2026-09-16 - CVE-2026-20306 published to NVD
2026-09-17 - Last updated in NVD database

Technical Details for CVE-2026-20306

Vulnerability Analysis

The vulnerability resides in the REST API exposed by the Cisco ISE and ISE-PIC web-based management interface. An authenticated attacker holding administrative credentials sends crafted HTTP requests containing malicious payloads in parameters that the API forwards to shell command execution. The API fails to neutralize special shell metacharacters before invoking the underlying operating system.

Exploitation yields arbitrary command execution in the context of the root account. On single-node deployments, exploitation can render the ISE node unavailable. Endpoints that have not previously authenticated cannot access the network until the node is restored, producing a network-wide denial-of-service condition against dependent services.

Root Cause

The root cause is improper validation of user-supplied input passed to REST API endpoints [CWE-78]. Input reaches OS command execution paths without adequate sanitization or use of safe parameterized invocation. Because the ISE management processes run with elevated privileges, injected commands inherit root-level authority.

Attack Vector

The attack vector is network-based. The attacker authenticates to the web-based management interface using valid administrative credentials, then issues crafted REST API requests to a vulnerable endpoint. Credential theft, credential reuse, or compromise of a legitimate administrator account can supply the required prerequisite access. No user interaction is required, and the scope is changed because the impact extends beyond the vulnerable component to the underlying operating system.

No public proof-of-concept code is available at the time of publication. Refer to the Cisco Security Advisory for vendor-authoritative technical detail.

Detection Methods for CVE-2026-20306

Indicators of Compromise

Unexpected child processes spawned by ISE web or API service accounts, particularly shells such as /bin/sh, /bin/bash, or utilities like curl, wget, nc, or python.
REST API requests to administrative endpoints containing shell metacharacters such as ;, |, &&, backticks, or $() in parameter values.
New or modified files in system directories, unexpected cron entries, or SUID binaries appearing after administrative API activity.
Outbound network connections from the ISE appliance to unfamiliar hosts following authenticated REST API sessions.

Detection Strategies

Correlate administrative authentication events with subsequent REST API calls that generate abnormal process trees on the ISE appliance.
Alert on any process execution under the ISE application service account that is not part of the documented baseline.
Inspect HTTP request bodies and query strings for command injection payload patterns targeting REST endpoints on TCP/443.

Monitoring Recommendations

Forward ISE application, audit, and syslog data to a centralized SIEM for behavioral correlation and long-term retention.
Enable and review REST API access logs, focusing on administrative account usage from unexpected source IPs or at unusual hours.
Monitor integrity of critical system binaries and configuration files on ISE nodes using file integrity monitoring.

How to Mitigate CVE-2026-20306

Immediate Actions Required

Apply the fixed software releases identified in the Cisco Security Advisory as the primary remediation.
Rotate credentials for all ISE and ISE-PIC administrative accounts and enforce multi-factor authentication on administrative logins.
Restrict network access to the ISE management interface using access control lists so that only trusted administrative subnets can reach the REST API.
Audit administrative activity in ISE logs for evidence of unauthorized REST API usage prior to patching.

Patch Information

Cisco has published fixed software versions and remediation guidance in the security advisory. Administrators should consult the Cisco Security Advisory cisco-sa-ise-cmd-inj-e2CuZCYZ to identify the fixed release for their deployed ISE or ISE-PIC train and plan an upgrade.

Workarounds

No vendor-provided workarounds are listed; upgrading to a fixed release is the recommended path.
Reduce risk by limiting administrative role assignments to the minimum number of accounts and reviewing role-based access control policies.
Segment the ISE management plane from general user and endpoint networks to shrink the reachable attack surface.

bash

# Example: restrict management access using an ACL applied to the ISE management interface upstream
# Replace 10.10.0.0/24 with your trusted administrative subnet
ip access-list extended ISE-MGMT-ACL
  permit tcp 10.10.0.0 0.0.0.255 host <ISE_MGMT_IP> eq 443
  deny   tcp any host <ISE_MGMT_IP> eq 443 log
  permit ip any any