CVE-2026-20352: Cisco Identity Services Engine RADIUS Denial of Service Vulnerability

Quick Answer

Cisco published a High-rated advisory that includes CVE-2026-20352, affecting Cisco Identity Services Engine (ISE) under the live advisory's conditions. Cisco does not separately state a CVE-specific Security Impact Rating (SIR); Common Vulnerability Scoring System (CVSS) base 8.6 (High). Confirm the exact platform, release, feature, and exposure; preserve relevant evidence; then follow Cisco's CVE-specific First Fixed guidance. Cisco reported no public announcement or malicious use for this CVE at the last check. That status and absence from CISA KEV are time-bounded and do not prove exploitation has never occurred.

Last verified: 2026-09-17 UTC from Cisco's advisory and CSAF record. Recheck both the affected-products and fixed-software sections before a production change.

Context

Status At A Glance

Product scope	Cisco Identity Services Engine (ISE)
CVE	CVE-2026-20352
TechGeeks response tier	P1 — urgent
Publication	New final Cisco advisory
First published	2026-09-16T16:00:00+00:00
Last updated	2026-09-16T16:00:00+00:00
Cisco advisory SIR	High
CVE-specific Cisco SIR	Not separately stated
CVSS base score / severity	8.6 — High
CVSS vector	CVSS v3.1 — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CISA KEV at last check	No — this is separate from Cisco severity and is not proof of no exploitation.
Cisco exploitation statement	The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

What Happened

A vulnerability in the RADIUS feature of Cisco Identity Services Engine (ISE) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper handling of certain RADIUS requests. An attacker could exploit this vulnerability by sending a crafted RADIUS request directly to an affected device. A successful exploit could allow the attacker to cause the ISE node to become unavailable. For single node deployments in that condition, endpoints that have not already authenticated would be unable to access the network until the node comes back up on its own. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is part of a group of advisories. For a complete list of the advisories and links to them, see Cisco Advance Notification for Publication of September 16, 2026, Security Advisories. In addition, for further documentation of improvements and fixes in Cisco Identity Services Engine, see Cisco Identity Services Engine Security Hardening Release: September 2026.

Affected Scope

This vulnerability affects Cisco ISE Policy Service Nodes (PSNs) if they have RADIUS services enabled. Note: RADIUS services are enabled by default. If Cisco ISE is being used for TACACS+ only, the network device is still affected by this vulnerability unless Session Services are turned off. Caution: Do not disable Session Services for RADIUS deployments because it will turn off all RADIUS services. For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory. Determine PSN and Session Services Configuration To determine whether a node in the Cisco ISE deployment is a PSN, use the following steps: Log in to the Cisco ISE web-based management interface. Click the menu icon. Choose Administration > System > Deployment > Deployment. Look under the General Settings tab. Look at the Policy Service section. If the slider is enabled, the node might be affected by this vulnerability. Continue to Step 6. If the slider is not enabled, the node is not affected by this vulnerability. Review the Enable Session Services check box. If the box is checked (Session Services enabled), the node is affected by this vulnerability. If the box is not checked (Session Services disabled), the node is not affected by this vulnerability. Caution: Do not disable Session Services for RADIUS nodes. It can be disabled for TACACS+ only nodes. All nodes in the deployment must be checked individually.

Match the exact hardware or virtual platform, installed train, patch level, enabled service, role, and management or data-plane exposure. A Cisco product-family name alone does not establish applicability.

Steps

What To Do Now

1. Confirm. Inventory Cisco Identity Services Engine (ISE) and record platform, exact release, patch level, enabled feature, role, and exposure.
2. Preserve. Save UTC context plus off-device authentication, management, firewall, network, endpoint, and SIEM evidence before logs rotate or a disruptive change removes context.
3. Scope. Compare each asset with the live Cisco advisory, including configuration prerequisites and exclusions.
4. Reduce exposure. Cisco documents no workaround for this CVE. Use only supported exposure controls while preparing the permanent fix.
5. Remediate. Confirm the affected product, release, and configuration. Cisco provides no workaround; reduce exposure where operationally feasible. Upgrade to the CVE-specific First Fixed release in Cisco's advisory table.
6. Validate. Confirm the resulting version, service health, logging, expected access, an expected denial, failover or cluster state, and representative dependent workflows.
7. Escalate. If evidence or exposure creates concern, open incident response and Cisco TAC recovery work rather than treating patch completion as proof of trust.

Fixed Releases And Mitigation

Investigation And Recovery

Review management authentication, account and privilege changes, API and web requests, configuration changes, crashes or restarts, resource pressure, and relevant external network telemetry for the vulnerable period. Preserve original evidence and follow Cisco TAC or incident-response guidance for containment, credential rotation, trusted rebuild, or service restoration when findings warrant it.

Notes

Exploitation Evidence

Cisco's exact status at the last check: The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

This CVE was not present in the TechGeeks CISA KEV snapshot at the last check. Cisco's 'not aware' statement and absence from KEV are time-bounded evidence, not claims that exploitation is impossible or has never happened. Severity and exploitation status remain separate signals.

Validation And Boundaries

This notice is documentation-backed. TechGeeks did not reproduce the exploit or independently test every fixed build. It does not prove that all members of the product family are affected, that the activity is widespread, that a clean indicator search excludes compromise, or that an update restored trust. Cisco's live advisory controls affected and fixed release information.

Related TechGeeks Resources

• TechGeeks Security Notice Center
• All Security Notices
• What to Do When a Device Hits CISA KEV
• Router CVE Exposure, Version, and Mitigation Checklist
• IoT Firmware Update and End-of-Support Checklist
• Live Protect and Runtime Vulnerability Shielding

References

• Cisco security advisory
• Cisco CSAF record
• Cisco September 16 publication notice
• NVD identifier record

Wrap-Up

Record whether CVE-2026-20352 applies. If it does, assign an owner and deadline appropriate to the High Cisco advisory SIR, preserve the evidence, complete Cisco's remediation, and document the validated result.

Correction policy: A material Cisco revision to scope, severity, exploitation status, workarounds, fixed software, or recovery guidance triggers an update and a new verification date.