CVE-2026-76423: Cisco ISE REST API Authentication Bypass Vulnerability
Tech GuruQuick Answer
CVE-2026-76423 exposes ISE and ISE-PIC configuration and identity data to unauthenticated REST API requests with administrative effect. Apply the CVE-specific Cisco fix and review API access. The Critical rating is clear, but Cisco's two published availability metrics conflict; the distinction remains documented below.
Fix Or Immediate Action
What to do now: 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.
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
Scope And Impact In Plain Language
Who should check: Operators of Cisco ISE and ISE-PIC, including exposure of their REST API. Inventory both products rather than relying on the shorter ISE family label in the status table.
When this applies: This vulnerability affects Cisco ISE and Cisco ISE-PIC, regardless of device configuration.
What could happen: An unauthenticated remote attacker may send a crafted request to the exposed REST API and read or modify configuration and identity data with administrative privileges. This is more than access to a sign-in page.
Not sure? Record the product, release, patch level, and REST API reachability. Cisco's structured vector uses A:L, while its narrative Details vector uses A:H; both source fields report 10.0. The page preserves that discrepancy rather than silently substituting a recalculated value. Use the vendor's Critical SIR and confirmed impact while seeking clarification.
Status At A Glance
| Product scope | Cisco Identity Services Engine (ISE) |
|---|---|
| CVE | CVE-2026-76423 |
| 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 | Critical |
| CVE-specific Cisco SIR | Critical |
| CVSS base score / severity | 10 — Critical |
| CVSS vector | CVSS v3.1 — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:L |
| 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 vulnerabilities that are described in this advisory. |
What Happened
Insufficient authorization checks on the exposed REST API allow a crafted HTTP request to read or modify configuration and identity data with administrative privileges. Cisco tracks the ISE/ISE-PIC defect as CSCwu39998. The structured CVSS vector uses A:L and the narrative uses A:H, both alongside a reported 10.0 score; no replacement vector is inferred here.
Affected Scope
This vulnerability affects Cisco ISE and Cisco ISE-PIC, regardless of device configuration.
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
- Confirm. Inventory Cisco Identity Services Engine (ISE) and record platform, exact release, patch level, enabled feature, role, and exposure.
- Preserve. Save UTC context plus off-device authentication, management, firewall, network, endpoint, and SIEM evidence before logs rotate or a disruptive change removes context.
- Scope. Compare each asset with the live Cisco advisory, including configuration prerequisites and exclusions.
- Reduce exposure. Cisco documents no workaround for this CVE. Use only supported exposure controls while preparing the permanent fix.
- 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.
- Validate. Confirm the resulting version, service health, logging, expected access, an expected denial, failover or cluster state, and representative dependent workflows.
- 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
Permanent Fix
Cisco method: Use the live advisory's CVE-specific First Fixed Release table.
No compact per-CVE fixed-release table is reproduced here because Cisco may use different First Fixed values by CVE and software train. Use this CVE's live advisory table or Cisco Software Checker; do not infer a fixed release from a combined hardening baseline or another Cisco notice.
Workaround Or Temporary Mitigation
No vendor workaround is documented for CVE-2026-76423. Use supported exposure controls only as temporary risk reduction while preparing the permanent software fix.
Important boundary: A workaround, ACL, exposure reduction, or service restriction can reduce risk while the update is prepared, but it does not patch the vulnerable code, prove every attack path is closed, or erase an earlier compromise.
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 vulnerabilities that are 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
Wrap-Up
Record whether CVE-2026-76423 applies. If it does, assign an owner and deadline appropriate to the Critical 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.
