Evidence used
- CISA confirms exploitation in the wild.
- Exploitation requires an existing local or physical foothold with privileges.
- EPSS is 81.11% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2021
CVE-2021-31955High confidence
Microsoft Windows Kernel Information Disclosure Vulnerability
Microsoft · Windows
5.5MediumCVSS 3.1
Patch now
Patch availableCISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityMedium→Operational priority:Critical, raised 2 bands.upgradedsince 3 Nov 2021
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict local access and enforce least privilege on affected hosts.
- Increase monitoring for the attack path and post-exploitation behaviour described in the report.
Verification
- Confirm that the asset runs Microsoft Windows and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.
Patch available01
What, why and how
Microsoft Windows Kernel contains an unspecified vulnerability that allows for information disclosure. Successful exploitation allows attackers to read the contents of kernel memory from a user-mode process.
What
Microsoft Windows Kernel contains an unspecified vulnerability that allows for information disclosure. Successful exploitation allows attackers to read the contents of kernel memory from a user-mode process.
Why
The product does not properly prevent sensitive system-level information from being accessed by unauthorized actors who do not have the same level of access to the underlying system as the product does.
How
An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may obtain information outside the intended access boundary.
What
Microsoft Windows Kernel contains an unspecified vulnerability that allows for information disclosure. Successful exploitation allows attackers to read the contents of kernel memory from a user-mode process.
Why
The product does not properly prevent sensitive system-level information from being accessed by unauthorized actors who do not have the same level of access to the underlying system as the product does.
How
An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may obtain information outside the intended access boundary.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation Confirmed in the wild
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2021-11-03.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.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 → Exposure of Sensitive System Information to an Unauthorized Control Sphere → obtain information outside the intended access boundary
- 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-497 ↗
CWE-497: Exposure of Sensitive System Information to an Unauthorized Control Sphere. The product does not properly prevent sensitive system-level information from being accessed by unauthorized actors who do not have the same level of access to the underlying system as the product does.
- 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:N/A:N/E:F/RL:O/RC:CCommon 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.INoneIntegrity impact: No direct loss is represented by this metric.ANoneAvailability impact: No direct loss is represented by this metric.- Post-exploitation / living off the land
- The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
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. - Patch available
- Affected
- Windows 10 Version 2004: 10.0.0 < 10.0.19041.1052
- Windows Server version 20H2: 10.0.0 < 10.0.19042.1052
- Windows 10 Version 20H2: 10.0.0 < 10.0.19042.1052
- Windows 10 Version 1909: 10.0.0 < 10.0.18363.1621
- Windows 10 Version 21H1: 10.0.0 < 10.0.19043.1052
- Windows Server 2019: 10.0.0 < 10.0.17763.1999
- Windows Server 2019 (Server Core installation): 10.0.0 < 10.0.17763.1999
- Windows 10 Version 1809: 10.0.0 < 10.0.17763.1999
- Windows Server version 2004: 10.0.0 < 10.0.19041.1052
- Action
- Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
- Workaround
- No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04
Evidence and provenance
Published 8 Jun 2021 · Last source change 21 Oct 2025, 23:25 UTC · CWE-497 · Exposure of Sensitive System Information to an Unauthorized Control Sphere
CVE recordCVE.org · 5.1
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-14
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2021-18828
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCISA ADP
NVD statusNVD enriched
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
- Affected versionsThe structured affected or fixed version information changed.CNA ↗
- Before
- 10.0.0 < 10.0.17763.1999; 10.0.0 < 10.0.18363.1621; 10.0.0 < 10.0.19043.1052; 10.0.0 < 10.0.19041.1052; 10.0.0 < 10.0.19042.1052 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- After
- Windows 10 Version 1809: 10.0.0 < 10.0.17763.1999; Windows Server 2019: 10.0.0 < 10.0.17763.1999; Windows Server 2019 (Server Core installation): 10.0.0 < 10.0.17763.1999; Windows 10 Version 1909: 10.0.0 < 10.0.18363.1621; Windows 10 Version 21H1: 10.0.0 < 10.0.19043.1052; Windows 10 Version 2004: 10.0.0 < 10.0.19041.1052; Windows Server version 2004: 10.0.0 < 10.0.19041.1052; Windows 10 Version 20H2: 10.0.0 < 10.0.19042.1052; Windows Server version 20H2: 10.0.0 < 10.0.19042.1052 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
CVE published
Added to CISA KEV
Fixed release or patch reference recorded
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.