Security readout for executives and security teams
Plain-English summary
A memory-safety flaw in Windows LSASS could let a low-privileged, authorized network attacker run code on affected systems without user interaction. Successful exploitation could compromise confidentiality, integrity, and availability. Exploitation is considered difficult, but LSASS is security-sensitive, making affected servers and endpoints important remediation targets.
Executive priority
Treat this as a high-priority patching issue, especially on reachable servers and identity-sensitive systems. High exploitation complexity reduces immediate likelihood, but low required privileges, network reachability, and potential full-system impact justify prompt inventory, controlled update deployment, and documented verification.
Technical view
CVE-2026-20854 is a CWE-416 use-after-free vulnerability in LSASS. Its CVSS 3.1 score is 7.5: network-accessible, high complexity, low privileges required, no user interaction, unchanged scope, and high impact across confidentiality, integrity, and availability. The supplied vector indicates unproven exploitation and an official fix.
Likely exposure
Exposure is identified for Windows 11 24H2 build 10.0.26100.0, Windows 11 25H2 build 10.0.26200.0, and Windows Server 2025 build 10.0.26100.0, including Server Core. Other products or versions are not established by the supplied evidence.
Exploitation context
The attacker must already be authorized with low privileges and reach the target over a network. Exploitation requires high complexity and no user interaction. The supplied record is not flagged as KEV, and the provided sources contain no evidence of active exploitation; the CVSS exploit-maturity metric is unproven.
Researcher notes
The supplied evidence establishes the vulnerable component, CWE, affected product builds, and CVSS characteristics, but provides no root-cause detail beyond use-after-free, affected protocol, attack preconditions beyond authorization, specific KB identifiers, or public proof of concept. Avoid inferring additional affected Windows releases or exploitability conditions.
Mitigation direction
- Review Microsoft's CVE advisory for the exact security update applicable to each affected product and build.
- Apply the applicable Microsoft security update through the organisation's approved patch-management process.
- Prioritize exposed Windows Server 2025 systems and security-sensitive infrastructure during deployment planning.
- If immediate updating is impossible, consult Microsoft guidance for supported temporary mitigations; none are specified in the bundle.
Validation and detection
- Inventory Windows 11 24H2, Windows 11 25H2, and Windows Server 2025 systems.
- Compare operating-system builds and installed updates with Microsoft's CVE advisory and update records.
- Confirm Server Core installations are included in assessment and remediation reporting.
- Recheck Microsoft's advisory for revisions because the supplied record was updated on 30 July 2026.
Public sources used
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-416: 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-20854 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
- High
- CVSS
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:L/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:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C1.65.9microsoftVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:H/PR:L/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
- Windows Local Security Authority Subsystem Service (LSASS) Remote Code Execution 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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.