Secure Boot Certificate Rotation 2023: OS Side Deployment and Troubleshooting

Microsoft’s Secure Boot certificate rotation is no routine patch — it is a coordinated, firmware‑adjacent program that replaces the 2011 signing certificates with a 2023 family of CAs, installs a new boot manager signed by that chain, and (optionally) applies revocations and Secure Version Number protections to prevent rollback attacks. This article explains exactly how the OS‑side deployment works, the tools IT teams can use (including the new WinCS CLI), the normal progression of registry bits and scheduled tasks, and practical troubleshooting for the two most common failure modes: KEK application failures and firmware‑returned errors.

Background​

Secure Boot enforces pre‑OS integrity by using a small set of trust anchors stored in firmware: the Platform Key (PK), Key Exchange Key (KEK), the allowed‑signatures database (DB), and the revoked signatures database (DBX). Several Microsoft‑provided certificates issued in 2011 — notably the Microsoft Corporation KEK CA 2011, Microsoft UEFI CA 2011, and Microsoft Windows Production PCA 2011 — are scheduled to expire starting in mid‑2026, with one principal bootloader CA expiring in October 2026. To avoid losing the ability to deliver boot‑time security fixes and to prevent breakage, Microsoft and OEM partners are rolling a replacement certificate family (the “2023” CAs) and an OS‑side deployment path that updates firmware variables where permitted. This program is deliberate, staged, and intentionally order sensitive because the wrong sequence can break updateability or create irreversible states on some devices.

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Overview: the OS‑side deployment model​

Microsoft’s delivery model for the 2023 CA family mixes firmware updates from OEMs with OS‑side actions delivered via Servicing Stack Updates (SSU) and Latest Cumulative Updates. On the Windows side a scheduled task (runs every 12 hours by default) inspects a bitmask called AvailableUpdates under the Secure Boot servicing registry area and processes specific bits that tell Windows which Secure Boot operations to attempt. Each bit corresponds to a specific firmware variable or OS operation; bits are processed in a strict order so trust anchors exist before trust‑dependent artifacts are changed. When an operation completes successfully, its bit is cleared. The special modifier bit 0x4000 is preserved to indicate the device’s prior trust posture.
Key operational notes:

• The scheduled Secure Boot update task runs every 12 hours and looks at the AvailableUpdates bitfield to decide what to do next.
• Enterprise guidance commonly uses the value 0x5944 to request the full enterprise update flow (add the 2023 CA entries, apply KEK, and deploy the new boot manager).

The bitfield (what each bit does — processed in this order)​

• Order 1 — 0x0040: Add Windows UEFI CA 2023 to the Secure Boot DB. This enables firmware to trust boot managers signed by the new Windows PCA.
• Order 2 — 0x0800: Add Microsoft UEFI CA 2023 to the DB. If the modifier 0x4000 is set, Windows will only add this if Microsoft Corporation UEFI CA 2011 is already present, preserving the device’s prior trust decision.
• Order 3 — 0x1000: Add Microsoft Option ROM CA 2023 to the DB (same conditional behavior if 0x4000 is set).
• Modifier — 0x4000: When present, instructs Windows to only apply the Microsoft UEFI CA 2023 and Microsoft Option ROM CA 2023 if the device previously trusted Microsoft Corporation UEFI CA 2011. This preserves the device’s security profile and prevents adding Microsoft certificates where the older 2011 CA was not trusted. Note: 0x4000 is not cleared at the end of processing — it remains as the final registry state in many flows.
• Order 4 — 0x0004: Look for a KEK object signed by the device’s PK and apply it into the firmware’s KEK variable. OEMs control the PK and must sign the new Microsoft KEK and return it to Microsoft so it can be included in servicing updates. If no OEM‑signed KEK exists for the platform, this step will fail and be retried.
• Order 5 — 0x0100: Deploy the boot manager signed by Windows UEFI CA 2023 to the boot partition (replacing the old Microsoft Windows Production PCA 2011–signed boot manager).

A typical progression on a device configured for the full enterprise flow looks like:

• Start with AvailableUpdates = 0x5944 (bits for the full flow).
• 0x0040 processed → cleared (Windows UEFI CA 2023 added).
• 0x0800 processed → cleared if condition passes (Microsoft UEFI CA 2023).
• 0x1000 processed → cleared similarly.
• 0x0004 processed → KEK applied (cleared on success).
• 0x0100 processed → boot manager replaced and corresponding bit cleared.
• Final key read often ends up as 0x4000 (the modifier bit preserved).

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Tools and commands: WinCS, registry triggers, and verification commands​

Microsoft provided several operational interfaces to make the flow auditable and scriptable:

• WinCS / WinCsFlags.exe (Windows Configuration System CLI) — a new small CLI exposing a named configuration key for administrators. The published configuration for deploying the Secure Boot 2023 CA set is Feature_AllKeysAndBootMgrByWinCS with WinCS key F33E0C8E002. You can query and apply this key (domain‑admin elevation required) so an admin can script and audit the OS side of the rollout across managed fleets. Use WinCsFlags.exe /query and /apply to operate.
• Registry trigger — administrators may set AvailableUpdates directly:
• Registry path: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecureBoot (or in some guidance under …\SecureBoot\Servicing). Setting AvailableUpdates to 0x5944 signals Windows to process the full enterprise update. After setting the registry, you may either wait for the scheduled task or force it.
• Force the scheduled Secure‑Boot update task (lab/testing only):
• Start the scheduled job: Start‑ScheduledTask -TaskName "\Microsoft\Windows\PI\Secure-Boot-Update".
• Or run WinCsFlags /apply -key "F33E0C8E002" to apply the WinCS configuration and let the scheduled task pick it up.
• Verification checks (PowerShell / system tools):
• Confirm Secure Boot is enabled: Confirm‑SecureBootUEFI (PowerShell, elevated).
• Inspect DB/DBX contents: Get‑SecureBootUEFI db and Get‑SecureBootUEFI dbx. Example quick string test: ::ASCII.GetString((Get‑SecureBootUEFI db).bytes) -match 'Windows UEFI CA 2023' returns True when the new CA is present.
• Check the AvailableUpdates registry value and the status keys UEFICA2023Status (NotStarted / InProgress / Updated) and UEFICA2023Error (0 = success) to track per‑device progress.

Use these tools to build scripted checks and telemetry reporting in your management platform (Intune, SCCM, WSUS, etc.). The WinCS flow is specifically designed to let IT orchestrate the initial OS‑side actions in a repeatable, auditable manner.

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Deployment playbook (practical, prioritized steps for IT)​

Treat this as a program, not a single patch. The rollout touches firmware, boot artifacts, and recovery tooling — that requires careful sequencing, backups, and pilot validation.

Phase 0 — Planning and inventory (day 0–14)​

• Inventory by OEM, model, firmware version, Secure Boot state, TPM presence, partition style (GPT vs MBR), and BitLocker state using msinfo32, Confirm‑SecureBootUEFI, and CMDB exports.
• Identify devices that are air‑gapped or block diagnostic telemetry (these will not receive Microsoft‑managed updates).

Phase 1 — Prepare recovery posture (immediately)​

• Export and verify BitLocker recovery keys are stored in AD/Azure AD or an audited vault. Changing Secure Boot or firmware can trigger recovery prompts.
• Build updated bootable recovery media (ISOs, USBs, PXE) and ensure they include the new boot manager or the ability to reapply the 2023 CA if needed.

Phase 2 — Pilot (2–6 weeks)​

• Pick a small, representative pilot across major OEMs and firmware families.
• Ensure the device has the servicing baseline (SSU + LCU containing Secure Boot payload).
• Apply WinCS or set AvailableUpdates = 0x5944 on pilot devices and force the scheduled task for observation. Use WinCsFlags /apply -key "F33E0C8E002" as an auditable way to signal the change.
• Validate: Confirm‑SecureBootUEFI; inspect Get‑SecureBootUEFI db for Windows UEFI CA 2023; monitor UEFICA2023Status and UEFICA2023Error; check event log TPM‑WMI events (IDs below).

Phase 3 — Staged rollout (6–20 weeks)​

• Roll out by OEM/firmware family in waves, monitoring logs and telemetry. Pause if a particular hardware family shows outliers (firmware variable write failures, unexpected BitLocker recoveries, or boot failures).

Phase 4 — Decide on DBX revocations and SVN (post‑validation)​

• Adding the old 2011 PCA entries to DBX and applying Secure Version Number (SVN) protections can be effectively irreversible on many firmware implementations. Only apply these enforcement steps after broad testing and OEM confirmation and after rebuilding all recovery/install media to the new signing chain.

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Troubleshooting: the two common failure modes and practical triage​

Symptom A — KEK update fails and never clears 0x0004 (AvailableUpdates remains 0x4104)​

What happens:

• The OS applies DB entries and boot manager changes but stalls on the KEK update (the 0x0004 bit remains set). Event ID 1796 is commonly logged when the driver/system encounters an unexpected per‑device failure during DB/DBX/KEK updates.

Why:

• The KEK object intended for a device must be signed by the device’s Platform Key (PK). The PK is controlled by the OEM. If the OEM has not produced or returned a KEK signed with the device’s PK for inclusion in Microsoft’s cumulative updates, Windows cannot apply the KEK. In other words, the failure is usually an OEM provisioning gap — not a Windows bug.

Triage steps:

• Check Event Viewer for TPM‑WMI events ID 1796 and inspect the error code text.
• Confirm AvailableUpdates value (HKLM\SYSTEM\CurrentControlSet\Control\SecureBoot\AvailableUpdates); if 0x0004 remains set after retries, escalate to OEM.
• Contact the OEM and request confirmation that a KEK signed with that device’s PK exists and was submitted to Microsoft for inclusion in the cumulative update. The OEM owns PK signing and delivery.
• If OEM cannot provide a signed KEK, consider compensating controls (isolation, hardware replacement) for devices of that model. Document these devices in an exceptions register.

Caveat: If you see Event ID 1796 but the error code or event text references firmware refusal, also follow the firmware error triage below.

Symptom B — Firmware returns error when writing variables (Event ID 1795)​

What happens:

• When Windows hands the certificate or KEK object to firmware, the firmware sometimes refuses the write or returns an error code (TPM‑WMI Event ID 1795 is logged). This is purely a firmware behavior: some firmware rejects OS‑initiated writes, enforces vendor policies, or has bugs that prevent variable writes.

Triage steps:

• Check Event Viewer for TPM‑WMI Event ID 1795 and capture the firmware error code included in the event. The event explicitly states the firmware returned an error and includes the code the platform returned.
• Validate whether the firmware vendor has published a UEFI update that enables OS variable writes or includes the 2023 CA set as factory defaults. If an OEM‑supplied firmware update exists, test and apply it in a controlled manner.
• Some platforms require a full power‑cycle (power off / disconnect battery for laptops) for firmware to commit variable writes. Reboot normally and, if recommended by the OEM, perform a full power cycle.
• If the device is virtualized, check whether the VM host or hypervisor exposes variable write support to guests; some VM images need the host‑side firmware updated.
• If OEM firmware is unavailable or refuses writes permanently, those devices must be tracked as exceptions and remediated by replacement or isolation.

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Event log map (quick reference)​

• Event ID 1034 — Secure Boot DBX update applied successfully.
• Event ID 1036 — Secure Boot DB update applied successfully.
• Event ID 1045 — Microsoft UEFI CA 2023 added to DB.
• Event ID 1795 — Firmware returned an error when attempting to update a Secure Boot variable. Check OEM firmware.
• Event ID 1796 — Unexpected Secure Boot variable update failure; often seen with KEK application problems tied to OEM PK signing.
• Event ID 1798 — DBX revocation rejected because current default boot app is still signed by the old PCA (safety check prevents breaking boot).
• Event ID 1808 — Informational: device has the required new Secure Boot certificates and the boot manager was updated.

Use these IDs in central log collection and alerting so support teams can triage automatically.

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Practical tips, guardrails, and governance​

• Inventory first, change carefully. Firmware diversity is the single largest operational risk; treat this as a program with pilot rings mapped to OEM/firmware families.
• Back up BitLocker keys and test recovery. Changing boot components commonly triggers recovery flows; do not roll out broadly without verified recovery images and stored keys.
• Update recovery and install media to include the new signing chain — otherwise devices may refuse older media after DBX/SVN changes.
• Delay DBX revocations and SVN enforcement until after wide validation. Those steps can lock you into states that are hard or impossible to revert. Plan communications and rollbacks accordingly.
• Document exceptions (models that never accept KEK/DB updates) and apply compensating controls such as network isolation, replacement lifecycle prioritization, or host‑based mitigations.

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Critical analysis: strengths, tradeoffs, and residual risks​

Strengths

• Auditable, scriptable flow: The Scheduled Task + AvailableUpdates bitfield, UEFICA2023Status/UEFICA2023Error keys, and WinCS CLI give enterprises deterministic, repeatable controls for the OS side of the rollout. That’s a major operational improvement over ad‑hoc firmware fiddling.
• Staged, safety‑aware ordering: The update sequence ensures trust anchors exist before switching to new signed artifacts and includes checks to prevent revocation when the default boot app would be broken. This reduces accidental mass‑bricking.

Tradeoffs and risks

• Firmware remains the gating factor. Many devices will need OEM firmware updates or vendor action. Where the firmware refuses OS variable writes, Microsoft’s OS‑side tooling cannot complete the job. Expect model‑level remediation plans.
• Irreversible enforcement steps. DBX revocations and SVN increases can be effectively permanent on many platforms — these must be delayed until you’re certain all recovery media and third‑party bootloaders have been updated.
• Third‑party and Linux impact. Distributions that rely on Microsoft‑signed shims may need to re‑sign shims or work with OEMs; dual‑boot fleets require extra coordination. Independent reporting has flagged nontrivial compatibility impacts for Linux users on older devices.

Unverifiable or vendor‑dependent facts (caution)

• Any claim about which exact device models will receive OEM firmware that permits variable writes must be verified directly with vendors. If a vendor‑specific statement appears in third‑party reporting without OEM confirmation, treat it as unverified and escalate to the OEM for confirmation.

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Recommended final checklist for deployment owners (copyable)​

• Inventory devices by OEM/model/firmware and mark Secure Boot on/off.
• Export and validate BitLocker recovery keys for all devices.
• Build updated recovery ISOs/USBs that are compatible with the 2023 signing chain.
• Stage a pilot across representative OEM firmware families. Apply WinCsFlags /apply -key "F33E0C8E002" or set AvailableUpdates = 0x5944 on pilots. Force the scheduled task and watch UEFICA2023Status/U EFICA2023Error.
• Monitor TPM‑WMI event logs (IDs 1034/1036/1045/1795/1796/1798/1808) centrally and escalate non‑zero UEFICA2023Error values.
• Coordinate OEM firmware updates for models that refuse OS writes and maintain an exceptions register for end‑of‑life or unpatchable devices.
• Only after broad validation apply DBX revocations and SVN enforcement; update all recovery media and rebuild images before enabling enforcement.

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Conclusion​

The Secure Boot certificate rotation is one of the most consequential platform‑level maintenance events enterprises will face in the next 12 months. Microsoft has provided an auditable, scriptable OS‑side flow — including the WinCS CLI and the AvailableUpdates bitfield — to help IT teams coordinate updates across large estates. However, the single largest operational dependency remains OEM firmware: if firmware refuses OS‑initiated variable writes or the OEM has not produced a KEK signed by the device PK, Windows cannot complete the KEK/DB/DBX updates and device‑level intervention will be required. Plan a measured, staged program: inventory, pilot, OEM coordination, updated recovery media, BitLocker backups, and conservative governance around irreversible revocations and SVN enforcement. The tools exist to do this safely; the hard work for IT teams will be the hardware and firmware validation that underpins a successful rollout.

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Source: Microsoft - Message Center Secure Boot Certificate updates: Guidance for IT professionals and organizations - Microsoft Support