Security readout for executives and security teams
Plain-English summary
Microsoft’s original 2011 Secure Boot certificates are expiring during 2026. Affected Windows devices need certificate trust updates to preserve Secure Boot protections. Firmware defects may cause those updates to fail or behave unpredictably, potentially weakening boot security or disrupting Secure Boot functionality.
Executive priority
Treat this as a time-bound platform-security maintenance program, not an immediate internet emergency. Prioritize inventory, firmware-diverse testing, and controlled deployment before the June and October 2026 expirations, especially for critical servers and difficult-to-recover devices.
Technical view
The affected certificates reside in UEFI KEK and DB stores and authorize trust-database updates, third-party boot components, and Windows Boot Manager. Microsoft rates the issue CVSS 6.4: exploitation requires local access, high privileges, and high complexity, but successful bypass could have high confidentiality, integrity, and availability impact.
Likely exposure
Exposure includes the listed Windows 10, Windows 11, and Windows Server releases where Secure Boot relies on affected 2011 certificate versions. Actual exposure depends on each device’s UEFI certificate state and whether certificate updates complete successfully.
Exploitation context
The bundle marks this CVE as not listed in KEV and provides no evidence of active exploitation. The CVSS vector describes local, high-privilege, high-complexity exploitation without user interaction.
Researcher notes
CWE-1329 and the CVSS vector indicate a security-feature bypass with demanding prerequisites but potentially severe impact. The central research concern is unreliable trust-store transition caused by firmware behavior. The supplied evidence does not identify particular firmware vendors, device models, exploit techniques, or confirmed exploitation.
Mitigation direction
- Inventory listed affected Windows client and server releases that use Secure Boot.
- Follow Microsoft’s CVE and Secure Boot certificate update guidance for approved trust updates.
- Test updates across representative firmware models before broad deployment.
- Stage rollout carefully because firmware defects can disrupt certificate trust updates.
- Complete certificate transitions before the relevant 2011 CA expiration dates.
Validation and detection
- Verify intended certificate updates are present in the UEFI KEK and DB stores.
- Confirm Secure Boot remains functional after updates on representative firmware models.
- Check certificate update status and investigate failures or unpredictable behavior.
- Validate Windows Boot Manager and authorized third-party boot components remain trusted.
- Track successful completion across every affected client and server release.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-1329: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-21265 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C0.55.9microsoftVulnerability scoring details
Base CVSS 3.1 score
6.4MediumVector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- Secure Boot Certificate Expiration Security Feature Bypass VulnerabilityCVE reference, microsoft · vendor-advisory, patch
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Reliance on Component That is Not Updateable
Reliance on Component That is Not Updateable represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.