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CVE-2026-76423 is a critical, unauthenticated remote authentication bypass in the Cisco ISE REST API. Cisco says a crafted HTTP request to an exposed REST API port could give an attacker administrative access to Cisco Identity Services Engine (ISE) or ISE Passive Identity Connector (ISE-PIC), including the ability to read or modify configuration and identity data. The priority is to identify the deployed release line and upgrade to its first fixed patch: Cisco says no workaround addresses the vulnerability.
There is an important limit for incident responders: Cisco’s September 16, 2026 advisory does not publish CVE-2026-76423-specific indicators of compromise or a detection and recovery playbook. Treat the hunting suggestions below as general investigation directions based on the described attack surface—not as Cisco-validated detection rules.
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What CVE-2026-76423 means for ISE administrators
Cisco identifies CVE-2026-76423 as an authentication bypass in the REST API. An unauthenticated remote attacker could send a crafted HTTP request to an exposed REST API port and gain administrative access. Cisco says successful exploitation could allow the attacker to read and modify ISE configuration and identity data with administrative privileges. Cisco rates the issue Critical, with a CVSS v3.1 base score of 10.0.
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Cisco lists ISE and ISE-PIC as affected regardless of device configuration. That does not establish that a particular deployment is reachable from the internet or has been exploited; it means administrators should check every applicable system against the affected release lines and remediate using Cisco’s fixed-release guidance. CVE-2026-76423 is one issue in a broader Cisco advisory. The other vulnerabilities in that advisory have different prerequisites and impacts and are not dependent on this one. Do not assume their fixes or risk descriptions apply to this authentication bypass. Read Cisco’s September 16, 2026 security advisory.
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- Firewall Protection Supported: Threat Protection
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- Firewall Protection Supported: Intrusion Prevention
- Total Number of Ports: 8
Which Cisco ISE patch fixes CVE-2026-76423?
Use the first-fixed release for the deployed ISE or ISE-PIC release line. These are Cisco’s listed first-fixed releases:
| Release line | First fixed release |
|---|---|
| 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 |
For releases earlier than 3.1, Cisco says to migrate to a fixed release in the table. Cisco also notes that ISE-PIC has reached end of sale and release 3.4 is its last supported release. Check the exact installed version, patch, and support status against the current Cisco advisory and Cisco product support channels before scheduling the upgrade.
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Upgrade access and support
Cisco recommends upgrading to the listed fixed software and states that no workaround addresses this vulnerability. If you bought directly from Cisco without a service contract, or bought through a third party and cannot obtain the fixed software through that point of sale, Cisco says to contact Cisco TAC with the product serial number and the advisory URL as evidence of upgrade entitlement. Entitlement depends on the purchase and support circumstances; do not assume every deployment has the same access route. Cisco TAC contact information.
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The primary advisory describes the attack as a crafted HTTP request directed at an exposed REST API port, but it does not provide a CVE-2026-76423-specific URI, username pattern, log filename, command, network signature, or other indicator. Cisco’s advisory therefore does not support a definitive detection rule or a claim that a particular log entry proves exploitation.
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As a practical hunt direction inferred from Cisco’s attack description, review available ISE and surrounding network telemetry for anomalous REST API activity, especially requests reaching the exposed API port that do not fit expected administrative or application traffic. Preserve relevant logs and records before routine retention or rotation removes them. Correlate observations across independent network and security systems where available. These are general investigative steps, not a Cisco-published CVE-specific recipe; the advisory does not establish which telemetry fields or patterns will reliably identify this attack.
Do not borrow indicators from CVE-2026-76460
Cisco has published access.log and suspicious-username guidance for CVE-2026-76460, a separate ISE authentication bypass. Its advice—including reviewing access.log on each node and considering that a root-level attacker may remove or hide evidence—belongs to that other vulnerability. It is not confirmed detection guidance for CVE-2026-76423. You can consult Cisco’s CVE-2026-76460 advisory as a distinct related notice, but verify with Cisco whether any of its directions apply to your CVE and ISE version before using them as a basis for conclusions.
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- CONFIGURABLE: With available Firepower Threat Defense (FTD) base software, add network-based content inspection, Intrusion Prevention System (IPS), and URL filtering
- PEACE OF MIND: 90-day limited warranty
What should you do if compromise is suspected?
Cisco’s CVE-2026-76423 advisory confirms the potential for administrative access and configuration and identity data modification, but it does not prescribe a containment, evidence-collection, re-imaging, credential-rotation, or recovery sequence. Do not treat a generic checklist as a vendor-validated recovery procedure for this CVE.
- Engage your organization’s incident-response process and involve the teams responsible for ISE and network security.
- Preserve available ISE and independent network or security telemetry, following your organization’s evidence-handling procedures.
- Contact Cisco support for current, deployment-specific guidance. Cisco TAC is also the route Cisco identifies for some customers who cannot obtain the fixed software through their point of sale.
- Plan remediation around the applicable first-fixed release, confirming the version, patch, and support status with Cisco before scheduling changes.
These are prudent general response recommendations, not steps Cisco specifically prescribes for CVE-2026-76423. Cisco’s advisory also made a publication-time statement about what PSIRT then knew regarding public announcements and malicious use; that dated statement does not establish the current exploitation status.
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