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CVE-2026-76423 – Unauthenticated REST API Admin Access (Authentication Bypass) – Cisco ISE 3.1–3.5 /

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Summary

CVE-2026-76423 is a critical authentication bypass vulnerability in the REST API of Cisco Identity Services Engine (ISE) and Cisco ISE Passive Identity Connector (ISE-PIC). Due to insufficient authorization checks in the REST API web service, an unauthenticated, remote attacker can send a crafted HTTP request to the exposed REST API port and gain full administrative access to the affected device. The vulnerability carries the maximum CVSS score of 10.0.

Technical details

  • Root cause: The REST API web service on Cisco ISE/ISE-PIC lacks proper authorization validation, allowing requests that should require administrator authentication to be processed without any credentials (CWE-290, Authentication Bypass by Spoofing).
  • Trigger conditions: The REST API must be reachable over the network; device configuration does not affect whether the device is vulnerable, and exploitation does not require any prior authentication or user interaction.
  • Attack vector: A remote attacker sends a crafted HTTP request directly to the exposed REST API port.
  • Impact: Successful exploitation grants administrative access, allowing an attacker to read and modify configuration and identity data managed by ISE — effectively taking full control of network access control policy for the organization.

Affected software

  • Cisco Identity Services Engine (ISE) Software — releases 3.1 through 3.5, including all patches prior to the fixed releases below
  • Cisco ISE Passive Identity Connector (ISE-PIC) — versions 3.1.0, 3.2.0, 3.3.0, 3.4.0, and 3.5.0

Severity

  • CVSS v3.1 Base Score: 10.0 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade to the first fixed release for your train:
    • 3.1 → 3.1 Patch 12
    • 3.2 → 3.2 Patch 11
    • 3.3 → 3.3 Patch 12
    • 3.4 → 3.4 Patch 7
    • 3.5 → 3.5 Patch 4
  • If no patch can be applied immediately: Cisco has stated there are no workarounds for this vulnerability. Restrict network access to the ISE REST API port to trusted management networks only, and avoid exposing the ISE administration/API interface directly to the internet until patched.

References

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