Security readout for executives and security teams
Plain-English summary
A flaw in Windows Remote Procedure Call can let an unauthorized attacker already operating locally expose sensitive information. It does not enable remote compromise, data modification, or service disruption according to the supplied CVSS assessment, but disclosed information could support further attacks.
Executive priority
Address through a prioritized patch cycle, accelerating systems with sensitive data, shared access, or plausible untrusted local execution. This is not supported as an emergency remote-exploitation event, but its high confidentiality impact warrants timely remediation and accountable tracking.
Technical view
CVE-2026-20821 is a CWE-200 information-disclosure vulnerability in Windows RPC. The CVSS 3.1 vector indicates local access, low complexity, no privileges, and no user interaction, with high confidentiality impact but no integrity or availability impact. The supplied score is 6.2.
Likely exposure
Exposure is limited to the listed Windows 10, Windows 11, and Windows Server versions, including identified Server Core installations. Risk is greater where unauthorized users can execute code locally or access shared systems containing sensitive information. The bundle does not specify vulnerable configurations or update KB numbers.
Exploitation context
The source bundle does not report active exploitation, and the CVE is not identified as CISA KEV. The CVSS exploit-maturity metric is unproven. Because exploitation requires local access, this is more likely to complement an existing foothold than provide initial remote entry.
Researcher notes
The supplied evidence establishes local, unauthenticated information disclosure but provides no disclosure mechanism, affected RPC interface, exploit proof, or observed attacks. Microsoft is the authoritative source for update applicability. Avoid inferring exposure beyond the explicitly listed products until detailed vendor guidance is reviewed.
Mitigation direction
- Inventory systems running the Windows products and versions named in the Microsoft advisory.
- Review Microsoft's CVE update guide for applicable security updates and product-specific instructions.
- Apply the applicable Microsoft security updates through the organization's tested patch process.
- Restrict untrusted local access while affected systems await remediation.
Validation and detection
- Compare operating-system editions and versions against Microsoft's affected-product list.
- Confirm applicable Microsoft security updates are installed and successfully reported by endpoint management.
- Reassess systems after patching to ensure no affected assets remain outstanding.
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-200: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. 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-2026-20821 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
- 6.2 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/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:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C2.53.6microsoftVulnerability scoring details
Base CVSS 3.1 score
6.2MediumVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/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
- Remote Procedure Call Information Disclosure 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.
Exposure of Sensitive Information to an Unauthorized Actor
Exposure of Sensitive Information to an Unauthorized Actor represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.