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Affected Environment
Cisco UCS Servers, UCS-based appliances, and UCS C-Series based appliances with UEFI Secure Boot enabled.
Threat Overview
A UEFI Shell vulnerability allows attackers to bypass Secure Boot protections and execute unauthorized software.
Exposure Timeline
Disclosed 9 September 2026, with fixed firmware releases available or scheduled through October 2026 across platforms.
Attack Surface
UEFI Shell boot option, reachable by authenticated users or attackers with physical or virtual KVM access.
Technical Root Cause
Availability of memory write commands in the UEFI Shell while Secure Boot is enabled on the device.
Exploitation Pathway
Attacker selects the UEFI Shell boot option and uses shell commands to overwrite Secure Boot related memory values.
Operational Impact
Successful exploitation allows execution of unauthorized software and compromises preboot environment integrity.
Strategic Impact
High risk across UCS server and appliance fleets given Secure Boot's role in preventing firmware level compromise.
Required Mitigation
Apply Cisco's fixed firmware releases across all affected UCS servers and appliances as scheduled.
Incident Response Guidance
Monitor for unexpected configuration changes, and forward logs to a centralized platform for analysis.
References
Cisco Security Advisory cisco-sa-ucs-uefi-sb-bypass-eb6xC5GW.
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