CVE Alert: CVE-2026-20293 – Cisco

A vulnerability in the Unified Extensible Firmware Interface (UEFI) Shell implementation of Cisco UCS Servers and UCS-based appliances could allow an authenticated attacker with valid credentials for a user account with the role of user or admin or an unauthenticated attacker with physical access to an affected device to bypass UEFI Secure Boot validation checks and execute unauthorized software. This vulnerability is due to the availability of memory write commands in the UEFI Shell while UEFI Secure Boot is enabled on a device. An attacker could exploit this vulnerability by selecting the UEFI Shell boot option at boot time and using available shell commands to modify UEFI memory variables. A successful exploit could allow the attacker to manipulate the preboot environment, overwrite UEFI Secure Boot-related memory values, and execute unauthorized software on the affected device.

## AI Summary Analysis

**Risk verdict:** High risk for exposed infrastructure, warranting expedited remediation because practical proof-of-concept code exists, although active exploitation, KEV inclusion and EPSS data are not provided.

**Why this matters:** Successful abuse can undermine platform trust at boot and run unauthorised code before the operating system and security tooling load. Likely objectives include persistent control, credential or workload compromise, disruption of hosted services, and using the server as a trusted foothold into management or production networks.

**Most likely attack path:** An attacker needs either valid low-privilege credentials or physical access, then selects the UEFI Shell during boot and alters protected memory values; no user interaction beyond the attacker’s actions is required. Remote exploitation is not indicated, but compromised management accounts could provide the starting point, while the unchanged scope limits direct impact to the affected system unless it is used to pivot.

**Who is most exposed:** Organisations operating UCS clusters, NFV platforms, standalone compute nodes or appliances in shared data centres are most at risk, particularly where broad administrator access, remote console capability or weak rack security is present.

Alert on unexpected UEFI Shell selection or boot-order changes.

Review firmware, boot and Secure Boot configuration changes.

Correlate unusual console access with privileged-account activity and reboots.

Validate measured-boot, firmware-integrity and platform-attestation results.

Investigate unauthorised pre-boot binaries or altered UEFI variables.

Mitigation and prioritisation:

Apply the vendor’s fixed firmware/software release on an expedited, risk-based change.

Restrict UEFI Shell, boot-device selection, remote console access and local console access.

Remove unnecessary user-role accounts; enforce MFA and least privilege.

Maintain physical protections and monitor maintenance-console access.

Confirm the remediation’s reboot and cluster failover impact before deployment; obtain EPSS and KEV status to refine priority.

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