CVE-2026-20293: Cisco UCS and UCS-Based Appliances UEFI Shell Secure Boot Bypass Vulnerability

01

What, why and how

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.

What

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.

Why

The product provides an Applications Programming Interface (API) or similar interface for interaction with external actors, but the interface includes a dangerous method or function that is not properly restricted.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

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.

Why

The product provides an Applications Programming Interface (API) or similar interface for interaction with external actors, but the interface includes a dangerous method or function that is not properly restricted.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation

?

Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.

No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material

?

Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.

None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path: local access → Exposed Dangerous Method or Function → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface: Local
Privileges required: Low: a basic authenticated account is required
User interaction: None
Attack complexity: Low: no specialised conditions are recorded
Security boundary: Unchanged: impact remains within the vulnerable component's security authority
Weakness ? CWE means Common Weakness Enumeration: a standard category for the underlying weakness.: CWE-749 ↗
CWE-749: Exposed Dangerous Method or Function. The product provides an Applications Programming Interface (API) or similar interface for interaction with external actors, but the interface includes a dangerous method or function that is not properly restricted.
CVSS vector ? CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land: Stolen credentials, tokens and legitimate administration functions may provide continued access without deploying a large custom toolset.

CWE-749

A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-72936Official EUVD mapping

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.

Official EUVD record ↗

BSI · German · WID-SEC-2026-3240Insyde UEFI Firmware und Cisco UCS (UEFI Shell Secure Boot): Schwachstelle ermöglicht Umgehen von Sicherheitsvorkehrungen

Ein Angreifer kann eine Schwachstelle in Insyde UEFI Firmware und Cisco Unified Computing System (UCS) ausnutzen, um den UEFI-Secure-Boot zu umgehen, die Pre-Boot-Umgebung zu manipulieren und beliebigen Code auszuführen.

Official advisory ↗

CERT-FR · French · CERTFR-2026-AVI-1138Vulnérabilité dans les produits Cisco

Une vulnérabilité a été découverte dans les produits Cisco. Elle permet à un attaquant de provoquer un contournement de la politique de sécurité.

Official advisory ↗

03

Patch and workaround

Operational remediation based on structured source evidence.

Status ? Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.: Fix not verified
Affected: Cisco Enterprise NFV Infrastructure Software: 4.1.1, 3.9.1, 3.5.2, 3.12.2, 3.6.2, 3.9.2, 3.11.3, 3.11.1, 3.5.1, 3.3.1, 3.10.2, 3.12.1b, 3.4.1, 3.12.1a, 3.6.3, 3.8.1, 3.11.2, 3.12.1, 3.12.3, 3.10.1, 3.6.1, 3.10.3, 3.7.1, 4.1.2, 4.2.1, 4.2.2, 4.4.1, 4.4.2, 4.5.1, 4.4.3, 4.6.1, 4.7.1, 4.6.2-FC2, 4.6.2, 4.8.1, 4.8.2, 4.9.1, 4.6.3, 4.9.2, 4.10.1, 4.9.3, 4.11.1, 4.9.4, 4.12.1, 4.6.4, 4.12.2, 4.13.1, 4.9.5, 4.12.3, 4.14.1, 4.6.3-FC4, 4.9.4-FC3, 4.12.4, 4.15.1, 4.9.6, 4.15.2, 4.12.5, 4.15.3, 4.15.4, 4.12.6, 4.15.5, 4.12.7, 4.12.8, 4.15.6, 4.9.10
Cisco Unified Computing System (Managed): 4.0(1a), 4.1(1a), 4.1(1b), 4.0(4h), 4.1(1c), 4.0(4e), 4.0(4g), 4.0(2e), 4.0(4a), 4.0(2d), 4.0(1b), 4.0(4f), 4.0(4c), 4.0(1c), 4.0(4b), 4.0(2b), 4.0(4d), 4.0(2a), 4.0(1d), 4.0(4i), 4.1(1d), 4.1(2a), 4.1(1e), 4.1(2b), 4.0(4k), 4.1(3a), 4.1(3b), 4.1(2c), 4.0(4l), 4.1(4a), 4.1(3c), 4.1(3d), 4.2(1c), 4.2(1d), 4.0(4m), 4.1(3e), 4.2(1f), 4.1(3f), 4.2(1i), 4.2(1k), 4.0(4n), 4.1(3h), 4.2(1l), 4.2(1m), 4.1(3i), 4.2(2a), 4.2(1n), 4.1(3j), 4.2(2c), 4.2(2d), 4.2(3b), 4.1(3k), 4.0(4o), 4.2(2e), 4.2(3d), 4.2(3e), 4.2(3g), 4.1(3l), 4.3(2b), 4.2(3h), 4.2(3i), 4.3(2c), 4.1(3m), 4.3(2e), 4.3(3a), 4.2(3j), 4.3(3c), 4.3(4a), 4.2(3k), 4.3(4b), 4.3(4c), 4.2(3l), 4.3(4d), 4.2(3m), 4.3(2f), 4.3(5a), 4.3(4e), 4.1(3n), 4.3(4f), 4.2(3n), 4.3(5c), 4.2(3o), 4.3(5d), 4.3(6a), 4.3(6b), 4.3(5e), 4.3(6c), 6.0(1b), 4.2(3p), 6.0(1c), 4.3(6d), 6.0(1d), 6.0(1e), 4.3(6e), 6.0(1f), 4.3(6f), 6.0(2b), 6.0(1h), 4.2(3r), 6.0(2c), 4.3(6g)
Cisco Unified Computing System (Standalone): 4.0(2g), 3.1(2i), 3.1(1d), 4.0(4i), 4.1(1c), 4.0(2c), 4.0(1e), 4.0(2h), 4.0(4h), 4.0(1h), 4.0(2l), 3.1(3g), 4.0(1.240), 4.0(2f), 4.0(1g), 4.0(2i), 3.1(3i), 4.0(4d), 4.1(1d), 3.1(3c), 4.0(4k), 3.1(2d), 3.1(3a), 3.1(3j), 4.0(2d), 4.1(1f), 4.0(4j), 4.0(2m), 4.0(2k), 4.0(1c), 4.0(4f), 4.0(4c), 3.1(3d), 3.1(2g), 3.1(2c), 4.0(1d), 3.1(2e), 4.0(1a), 4.0(1b), 3.1(3b), 4.0(4b), 3.1(2b), 4.0(4e), 3.1(3h), 4.0(4l), 4.1(1g), 4.1(2a), 4.0(2n), 4.1(1h), 3.1(3k), 4.1(2b), 4.0(2o), 4.0(4m), 4.1(2d), 4.1(3b), 4.0(2p), 4.1(2e), 4.1(2f), 4.0(4n), 4.0(2q), 4.1(3c), 4.0(2r), 4.1(3d), 4.1(2g), 4.1(2h), 4.1(3g), 4.1(3f), 4.1(2j), 4.1(2k), 4.1(3h), 4.2(2a), 4.1(3i), 4.2(2f), 4.2(2g), 4.2(3b), 4.1(3l), 4.2(3d), 4.3(1.230097), 4.2(1e), 4.2(1b), 4.2(1j), 4.2(1i), 4.2(1f), 4.2(1a), 4.2(1c), 4.2(1g), 4.3(1.230124), 4.1(2l), 4.2(3e), 4.3(1.230138), 4.2(3g), 4.3(2.230207), 4.2(3h), 4.2(3i), 4.3(2.230270), 4.1(3m), 4.1(2m), 4.3(2.240002), 4.3(3.240022), 4.2(3j), 4.1(3n), 4.3(2.240009), 4.3(3.240041), 4.2(3k), 4.3(3.240043), 4.3(4.240142), 4.3(2.240037), 4.3(2.240053), 4.3(4.240152), 4.2(3l), 4.3(2.240077), 4.3(4.242028), 4.3(4.241063), 4.3(4.242038), 4.2(3m), 4.3(2.240090), 4.3(5.240021), 4.3(2.240107), 4.3(4.242066), 4.2(3n), 4.3(5.250001), 4.2(3o), 4.3(2.250016), 4.3(2.250021), 4.3(5.250030), 4.3(2.250022), 4.3(6.250039), 4.3(6.250040), 4.3(5.250033), 4.3(6.250044), 4.3(6.250053), 4.3(2.250037), 4.3(2.250045), 4.3(4.252001), 4.3(4.252002), 6.0(1.250127), 4.2(3p), 6.0(1.250131), 4.3(6.250101), 6.0(1.250174), 4.3(6.250117), 4.3(5.250043), 4.3(5.250045), 4.3(6.250060), 6.0(1.250130), 4.3(4.241014), 6.0(1.251030), 4.3(2.250063), 6.0(1.250192), 4.3(6.260003), 6.0(1.250194), 6.0(1.260001), 4.3(6.260017), 4.3(2.260007), 6.0(2.260044), 6.0(2.260042), 4.0(1.260003), 2.0(2.260062), 2.0(1.250127), 2.0(1.250096), 4.0(1.260004), 6.0(2.260026), 6.0(1.251006), 1.2(0.250011), 1.1(0.250016), 1.0(0.240001), 1.0(0.250003), 1.2(0.250013), 1.1(0.250026), 1.0(1.250002), 1.1(0.250022), 1.1(0.250025), 1.0(1.250032), 6.0(2.260034), 6.0(2.260069), 4.3(6.260033), 2.0(2.260101), 4.2(3q), 4.2(3r), 1.2(0.260005)
Cisco Unified Computing System E-Series Software (UCSE): 4.11.1, 4.12.1, 4.12.2, 4.15.2, 4.15.3, 4.15.4
Fixed: No fixed version is explicitly recorded in the structured CVE data.
Action: No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround: No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.

04

Evidence and provenance

Published 8 Sept 2026 · Last source change 11 Sept 2026, 13:46 UTC · CWE-749 · Exposed Dangerous Method or Function

CVE recordCVE.org · 5.2

CVSS sourceCNA

EPSS source

?

The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.

FIRST · tracked since 2026-09-09

European sourceENISA EUVD · EUVD-2026-72936

Product sourceCNA

Remediation sourceCVE/CNA references

CWE sourceCNA

NVD statusNVD awaiting enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗

8 Sept 2026, 18:57 UTC
ENISA EUVD mappingEUVD-2026-72936 was added to the official ENISA EUVD mapping for this CVE.
Before
not recorded
After
{"euvdId":"EUVD-2026-72936"}
ENISA EUVD ↗
8 Sept 2026, 16:04 UTC
Catalogue recordCVE added to the BlackTree catalogue.
CNA ↗

2026-09-08CVE published

ENISA EUVD · EUVD-2026-72936↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗

Cisco UCS and UCS-Based Appliances UEFI Shell Secure Boot Bypass Vulnerability

National CERT insights
?
CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

ENISA European Vulnerability Database

EUVD-2026-72936

What, why and how

Exploit reality and attack path

Official authority intelligence

Patch and workaround

Evidence and provenance

What changed after publication

Cisco UCS and UCS-Based Appliances UEFI Shell Secure Boot Bypass Vulnerability

National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

EUVD-2026-72936

What, why and how

Exploit reality and attack path

Official authority intelligence

Patch and workaround

Evidence and provenance

National CERT insights
?
CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.