CVE-2026-20293: Cisco UCS Secure Boot Bypass Requires Auth or Physical Access, No Workarounds Exist

Cisco identified a high-severity vulnerability in its Unified Computing System servers and related appliances that compromises preboot security controls. The flaw, tracked as CVE-2026-20293, allows attackers to bypass UEFI Secure Boot validation checks and execute unauthorized software on affected devices.

The issue stems from memory write commands remaining available in the UEFI Shell even when Secure Boot is enabled. An attacker can select the UEFI Shell boot option and use these commands to modify UEFI memory variables. This manipulation overwrites Secure Boot-related values, effectively disabling the protection mechanism before the operating system loads.

Exploitation requirements

Exploitation requires either physical access to the device or valid credentials for a user account with user or admin roles. For Cisco UCS servers, an attacker with valid credentials for a user or admin account can exploit the vulnerability. For certain UCS-based appliances, physical access to the keyboard, video, and mouse interface is required, which limits the attack surface for those specific products.

Affected products

The vulnerability impacts 5000 Series Enterprise Network Compute Systems if they have UEFI Secure Boot enabled and run a vulnerable BIOS version. It also affects Cisco appliances based on preconfigured UCS C-Series Servers, including Application Policy Infrastructure Controller servers and Secure Firewall Management Center appliances, provided they support Secure Boot and expose KVM or virtual KVM console access.

Defender's checklist

Cisco has released software updates that address this vulnerability by removing memory modification commands from the UEFI Shell when Secure Boot is enabled. Organizations should verify their current BIOS versions against the fixed releases listed in the advisory. There are no workarounds available, so applying the vendor-provided update is the only confirmed mitigation for this high-severity risk.

Operational impact

Security teams should immediately inventory all Cisco UCS hardware and appliances to determine exposure. IT operations must coordinate with procurement to prioritize firmware updates for critical infrastructure. Leadership should be briefed on the risk of preboot compromise, which could undermine trust in the entire boot chain. Vendor support contacts should be engaged to confirm update availability for specific appliance models.

What to do and how to stay safe: Cisco

• Audit your environment to identify all Cisco UCS servers and appliances running vulnerable BIOS versions.
• Schedule downtime to apply the latest firmware updates provided by Cisco to patch the UEFI Shell flaw.
• Restrict physical access to server rooms and disable unnecessary KVM or virtual console access for appliances.
• Review user permissions to ensure only essential personnel have admin or user roles on affected management interfaces.

Step-by-step guide: Patch Management vs Vulnerability Management: The Critical Distinction

General security guidance from the InfoSec Ledger newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

What is the CVSS score for this vulnerability?

The base CVSS score is 7.1, which Cisco rates as a high security impact.

Are there any workarounds for CVE-2026-20293?

No, Cisco states there are no workarounds that address this vulnerability.

Which specific Cisco appliances are affected?

Application Policy Infrastructure Controller servers and Secure Firewall Management Center appliances are affected if they support UEFI Secure Boot.