Evidence used
- No CISA KEV confirmation is currently recorded.
- EPSS is 2.56% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2021
CVE-2021-31958High confidence
Windows NTLM Elevation of Privilege Vulnerability
Microsoft · Windows 10 Version 1809
7.5HighCVSS 3.1
Within 7 days
Patch availableHigh technical severity; prioritise exposed affected systems while verifying vendor guidance.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityHigh→Operational priority:High, unchanged from published severity.unchanged
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs Microsoft Windows 10 Version 1809 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.
High technical severity; prioritise exposed affected systems while verifying vendor guidance.
Patch available01
What, why and how
Windows NTLM Elevation of Privilege Vulnerability
What
Windows NTLM Elevation of Privilege Vulnerability
Why
A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes).
How
An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may gain additional privileges.
What
Windows NTLM Elevation of Privilege Vulnerability
Why
A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes).
How
An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may gain additional privileges.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
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
- a network path → Authentication Bypass by Capture-replay → gain additional privileges
- Attack surface
- Network
- Privileges required
- None: unauthenticated exploitation is possible
- User interaction
- Required interaction required
- Attack complexity
- High: exploitation depends on specific conditions
- 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-294 ↗
CWE-294: Authentication Bypass by Capture-replay. A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes).
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:CCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.- Post-exploitation / living off the land
- No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
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 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
- Windows 10 Version 1507: 10.0.0 < 10.0.10240.18967
- Windows 10 Version 1607: 10.0.0 < 10.0.14393.4467
- Windows Server 2016: 10.0.0 < 10.0.14393.4467
- Windows Server 2016 (Server Core installation): 10.0.0 < 10.0.14393.4467
- Windows 7: 6.1.0 < 6.1.7601.25632
- Windows 7 Service Pack 1: 6.1.0 < 6.1.7601.25632
- Windows 8.1: 6.3.0 < 6.3.9600.20045, 6.3.0 < 6.3.9600.20044
- Windows Server 2008 Service Pack 2: 6.0.0 < 6.0.6003.21137
- Windows Server 2008 Service Pack 2 (Server Core installation): 6.0.0 < 6.0.6003.21137
- Windows Server 2008 Service Pack 2: 6.0.0 < 6.0.6003.21137
- Windows Server 2008 R2 Service Pack 1: 6.1.0 < 6.1.7601.25632
- Windows Server 2008 R2 Service Pack 1 (Server Core installation): 6.0.0 < 6.1.7601.25632
- Windows Server 2012: 6.2.0 < 6.2.9200.23372
- Windows Server 2012 (Server Core installation): 6.2.0 < 6.2.9200.23372
- Windows Server 2012 R2: 6.3.0 < 6.3.9600.20045, 6.3.0 < 6.3.9600.20044
- Windows Server 2012 R2 (Server Core installation): 6.3.0 < 6.3.9600.20045, 6.3.0 < 6.3.9600.20044
- Action
- Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
- Workaround
- No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 8 Jun 2021 · Last source change 3 Aug 2024, 23:10 UTC · CWE-294 · Authentication Bypass by Capture-replay
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-2021-18830
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceNIST NVD
NVD statusNVD modified after enrichment
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.
CVE published
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.