CISCO: 📌 Reference: Cisco Security Advisory – Cisco UCS and UCS-Based Appliances UEFI Shell Secure Boot Bypass Vulnerability

CISCO Security Advisory

Published Date: Not specified

CVE: CVE-2026-20293

Advisory Summary

🗓️ Oct 13, 2026

🔐 ⚠️ Cisco UCS UEFI Secure Boot Bypass — High Severity
Cisco has disclosed a High security vulnerability affecting Cisco UCS Servers and UCS-based appliances. The issue resides in the UEFI Shell implementation, where an attacker may be able to bypass UEFI Secure Boot validation and execute unauthorized software.

• UEFI Shell memory write commands are available even when UEFI Secure Boot is enabled
• This enables manipulation of preboot/UEFI memory variables, potentially overwriting values used by Secure Boot controls

• Authenticated attackers with valid credentials for accounts with role user or admin
• Unauthenticated attackers with physical access to the affected device
• Exploitation path: attacker selects the UEFI Shell boot option and uses available commands to alter UEFI variables

• Potential execution of unauthorized code at the preboot stage
• Increased risk of rootkit/firmware-level persistence, since Secure Boot assurances may be undermined

• ✅ Cisco has released software updates to address the vulnerability.
• 🚫 No workarounds are provided.

• CVE-2026-20293

• Apply the Cisco-provided updates immediately for all impacted UCS and UCS-based appliances in scope.
• Audit for physical access exposure (data center entry controls, device lock-down, port/console protections).
• For UCS environments, review whether UEFI Shell access pathways could be exposed to lesser-privileged users and tighten:
• boot-time access controls
• user credential governance for roles that include user/admin

⛔ Operational note
Because Secure Boot is central to boot integrity, treat this as a serious preboot trust compromise risk and prioritize patching in the next maintenance window (or sooner if you operate high-threat or high-exposure systems).

-2026-20293

Reference: Vendor Advisory