Cisco Security Advisory
Cisco UCS and UCS-Based Appliances UEFI Shell Secure Boot Bypass Vulnerability
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CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N/E:X/RL:X/RC:X
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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.
Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ucs-uefi-sb-bypass-eb6xC5GW
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Vulnerable Products
This vulnerability affects the following Cisco products if they have UEFI Secure Boot enabled and are running a vulnerable BIOS version:
- 5000 Series Enterprise Network Compute Systems (ENCS) (CSCwu42927)
- UCS B-Series Blade Servers (CSCwt77804)
- UCS C-Series Rack Servers (CSCwt77804)
- UCS C845A M8 Rack Server (CSCwt77950)
- UCS C885A M8 Rack Server (CSCwt77952)
- UCS C880A M8 Rack Server (CSCwt78022)
- UCS E-Series M3 Servers (CSCwu42927)
- UCS E-Series M6 Servers (CSCwu42928)
- UCS S-Series Storage Servers (CSCwt77804)
- UCS X-Series Modular System (CSCwt77804)
- Unified Edge (CSCwt77804)
Cisco appliances that are based on a preconfigured version of a Cisco UCS C-Series Server are also affected by this vulnerability if they support UEFI Secure Boot and expose access to the keyboard, video, and mouse (KVM) or virtual KVM console. At the time of publication, this included the following Cisco products:
- Application Policy Infrastructure Controller (APIC) Servers
- Cisco Telemetry Broker Appliances
- HyperFlex Edge Nodes
- HyperFlex Nodes
- IEC6400 Edge Compute Appliances
- IOS XRv 9000 M7 Appliances
- Nexus Dashboard Appliances
- Secure Email Gateways1
- Secure Email and Web Manager1
- Secure Endpoint Private Cloud Appliances
- Secure Firewall Management Center (FMC) Appliances
- Secure Malware Analytics Appliances
- Secure Network Analytics Appliances
- Secure Network Server (ISE SNS) Appliances
- Secure Web Appliances1
1. Physical KVM access is required to exploit the vulnerability on these appliances, which significantly reduces the attack vector on these platforms.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
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The UEFI Shell is a command line interface that provides commands to debug, script, and control various booting options. It is available as a boot option on Cisco UCS Servers that are in UEFI boot mode.
The UEFI Shell includes multiple commands that allow memory modifications. When UEFI Secure Boot is enabled on a device, the availability of such commands could allow an attacker to manipulate the preboot environment, including the possibility of overwriting UEFI Secure Boot-related memory values, effectively bypassing UEFI Secure Boot validations.
As a resolution for this vulnerability, UEFI Shell commands that allow memory modifications are removed from the shell when UEFI Secure Boot is enabled on a device.
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There are no workarounds that address this vulnerability.
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Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To remediate this vulnerability and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.
Fixed Releases
In the following tables, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.
5000 Series ENCS
Note: Upgrading Cisco Integrated Management Controller (IMC) and BIOS on Cisco 5000 Series ENCS requires upgrading Cisco Enterprise NFV Infrastructure Software (NFVIS) on the platforms. Cisco IMC and BIOS are upgraded as part of the firmware auto-upgrade process.
Cisco NFVIS Release First Fixed Release 4.15 and earlier 4.15.7 (Oct 2026) UCS B-Series and X-Series Servers in UCS Manager Mode
Cisco UCS Server Software Release First Fixed Release Earlier than 4.3 Migrate to a fixed release. 4.3 4.3(6h)1 6.0 6.0(2d)1 1. These releases do not include a fix for Cisco UCS B-Series M5 Servers. A fix for these platforms will be included in upcoming releases (September 2026).UCS B-Series Servers in Intersight Managed Mode
Cisco Intersight Server Firmware Release First Fixed Release Earlier than 5.4 Migrate to a fixed release. 5.4 5.4(0.260050)1 6.0 6.0(2.260143) 1. This release does not include a fix for Cisco UCS B-Series M5 Servers. A fix for these platforms will be included in an upcoming release (September 2026).UCS X-Series Servers in Intersight Managed Mode
Cisco Intersight Server Firmware Release First Fixed Release Earlier than 5.4 Migrate to a fixed release. 5.4 5.4(0.260042) 6.0 6.0(2.260143) UCS C845A M8 Rack Server
Cisco UCS Server Software Release First Fixed Release 2.0 Release no. TBD (Oct 2026) UCS C880A M8 Rack Server
Cisco UCS Server Software Release First Fixed Release 4.0 4.0(2.260004) UCS C885A M8 Rack Server
Cisco UCS Server Software Release First Fixed Release 1.2 and earlier Release no. TBD (Sep 2026) UCS C-Series M5 Rack Servers in Standalone Mode or Intersight Managed Mode
Cisco UCS Server Software Release First Fixed Release Earlier than 4.2 Migrate to a fixed release. 4.2 4.2(3r) 4.3 4.3(2.260020) UCS C-Series M6, M7, M8 Rack Servers in Standalone Mode or Intersight Managed Mode
Cisco UCS Server Software Release First Fixed Release Earlier than 4.2 Migrate to a fixed release. 4.2 4.2(3r) 4.3 4.3(6.260054) 6.0 6.0(2.260143)1 1. The fixed 6.0(2.260143) Host Upgrade Utility (HUU) ISO release includes the Cisco IMC 6.0(2.260094) packaged release. After upgrading to this fixed release, the Cisco IMC UI Dashboard page will display the Firmware Version as 6.0(2.260094). The Last HSU bundle used field under Administration > Firmware Management will display the fixed 6.0(2.260143) release.UCS C-Series Servers in UCS Manager Mode
Cisco UCS Server Software Release First Fixed Release Earlier than 4.2 Migrate to a fixed release. 4.2 4.2(3s) 4.3 4.3(6h)1 6.0 6.0(2d)1 1. These releases do not include a fix for Cisco UCS C-Series M5 Servers. A fix for these platforms will be included in upcoming releases (September 2026).UCS E-Series M3 Servers
Cisco UCSE BIOS Release First Fixed Release 4.0 and earlier 4.041 (Sep 2026) 1. The fixed 4.04 BIOS release can be installed on UCS E-Series M3 Servers that are running any Cisco IMC 3.2 release using the steps in the Managing Firmware section of the Cisco UCS E-Series Integrated Management Controller GUI Configuration Guide.UCS E-Series M6 Servers
Cisco UCSE Software Release First Fixed Release 4.15 and earlier 4.15.4-b1 (Sep 2026) 1. The fixed 4.15.4-b Host Upgrade Utility (HUU) ISO release includes the fixed 2.06 BIOS release.UCS S-Series Storage Server
Cisco UCS Server Software Release First Fixed Release Earlier than 4.3 Migrate to a fixed release. 4.3 4.3(6.260054) Unified Edge
Cisco UCS XE-Series Server Firmware Release First Fixed Release 6.0 6.0(2.260143) Note: For Cisco appliances that are based on a preconfigured version of a Cisco UCS C-Series Server, administrators can perform a direct upgrade of the Cisco IMC and BIOS software using one of the fixed releases mentioned in the preceding tables. For instructions, see the Cisco Host Upgrade Utility User Guide. The exceptions are the appliances that are listed in the following table. For these appliances, follow the instructions in the Remediation column:
Cisco Hardware Platform First Fixed Firmware Release Remediation Cisco Telemetry Broker Appliances 6.0(2.260143)1 Install the firmware update CTB-FIRMWARE-6.0.2.260143-M6.iso. IEC6400 Edge Compute Appliances 4.3(6.260054) Apply the HUU upgrade using IEC6400-HUU-4.3.6-260054.img. IOS XRv 9000 M7 Appliances 6.0(2.260143)1 Install the firmware update package xrv9k-ucs-c220m7-huu-container-6.0.2.260143.tar.gz. Secure Email Gateways 4.3(2.260020) Install the firmware update package (Oct 2026). Secure Email and Web Manager 4.3(2.260020) Install the firmware update package (Oct 2026). Secure Endpoint Private Cloud Appliances 4.3(2.260020) (M5)
4.3(6.260054) (M6)Follow the steps documented in the TechNote. Secure Firewall Management Center (FMC) Appliances 4.3(2.260020) (M5)
6.0(2.260143)1 (M6, M8)Apply the Hotfix GA. Secure Malware Analytics Appliances 4.3(2.260020) (M5)
4.3(6.260054) (M6)Update the firmware using the Out-of-Band Firmware Update ISO procedure. Secure Network Analytics Appliances 4.3(2.260020) (M5)
6.0(2.260143)1 (M6)For M5, install the firmware update patch-common-SNA-FIRMWARE-4.3.2.260020-M5-v2-01.swu.
For M6, install the firmware update patch-common-SNA-FIRMWARE-6.0.2260143-M6-v2-01.swu.Secure Network Server (ISE SNS) Appliances 4.3(2.260020) (M5)
6.0(2.260143)1 (M6, M8)Apply the BIOS and HUU upgrade, as documented in Firmware Upgrade Guide for Cisco Secure Network Server 3600 Series, Cisco Secure Network Server 3700 Series, or Cisco Secure Network Server 3800 Series. Secure Web Appliances 4.2(3r) (M5)
4.3(6.260054) (M6)Install the firmware update package (Oct 2026). 1. The fixed 6.0(2.260143) firmware release includes the Cisco IMC 6.0(2.260094) packaged release. After upgrading to this fixed release, the Cisco IMC UI Dashboard page will display the Firmware Version as 6.0(2.260094). The Last HSU bundle used field under Administration > Firmware Management may display the fixed 6.0(2.260143) release or N/A, depending on the specific appliance and remediation used.The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.
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The Cisco PSIRT is aware that proof-of-concept exploit code is available for the vulnerability described in this advisory.
The Cisco PSIRT is not aware of any malicious use of the vulnerability that is described in this advisory.
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Cisco would like to thank Stas Lyakhov from Eclypsium for reporting this vulnerability.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
For additional information on Cisco's vulnerability management, disclosure cadence, and software patching strategy, see Cisco's Transition to a Risk-Based Vulnerability Disclosure Model.
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Show LessVersion Description Section Status Date 1.1 Updated remediation for IOS XRv 9000 M7 Appliances. Fixed Releases Final 2026-SEP-15 1.0 Initial public release. - Final 2026-SEP-08
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SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT
The Cisco Support and Downloads page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid.
Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC). Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.
When considering software upgrades, customers are advised to regularly consult the advisories for the relevant Cisco products to determine exposure and a complete upgrade solution. In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
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Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy for more information.