Windows
CVE-2026-21240
HIGH
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessLocal login with standard user privileges
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ExploitTrigger race condition in HTTP.sys kernel driver
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ExecutionManipulate file handles between validation and use
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ImpactElevate to SYSTEM privileges
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A04:2021 - Insecure Design
ASVS 5.0
V15 - Secure Coding and Architecture TOCTOU prevention
|
| Exploitation Conditions | Local user account with login privileges required. Windows HTTP.sys kernel driver must be active (default on Windows Server with IIS or HTTP API usage). No network access required; exploitation is local-only. |
| Impact | CVSS 7.8 (HIGH). Attack vector: Local. Complexity: Low. Privileges required: Low. User interaction: None. Exploitable via local access. |
| Exploit ScenarioDerived | An attacker could exploit this vulnerability to compromise the affected system. |
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Alert meAnalysisAIv1 – Mar 12, 2026
Windows HTTP.sys contains a race condition between privilege checks and resource access that enables local authenticated users to escalate privileges on Windows 10 21H2, Windows 11 23H2, and Windows Server 2025. An attacker with valid credentials can exploit this timing vulnerability to gain system-level access. No patch is currently available for this vulnerability.
Earlier versions of this analysis (1)
Time-of-check time-of-use (toctou) race condition in Windows HTTP.sys allows an authorized attacker to elevate privileges locally. [CVSS 7.8 HIGH]
RemediationAI
Monitor vendor advisories for a patch.
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 11 packages in microsoft
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Affects Windows 10 1809. Time-of-check time-of-use (toctou) race condition in Windows HTTP.sys allows an authorized attacker to elevate privileges locally.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionCVE.org
Time-of-check time-of-use (toctou) race condition in Windows HTTP.sys allows an authorized attacker to elevate privileges locally.
Executive ViewAI
A privilege escalation vulnerability in Windows HTTP.sys enables authorized local users to gain elevated system access. This affects organizations running Windows servers and could allow internal threats or compromised user accounts to achieve administrator-level control, potentially leading to data breach, system compromise, or lateral movement across the network.
Implement strict local access controls and principle of least privilege to reduce authorized users who could exploit this vulnerability; disable HTTP.sys features not in active use; segment networks to limit lateral movement if privilege escalation occurs; deploy endpoint detection and response (EDR) tools to monitor for suspicious privilege escalation attempts; enforce multi-factor authentication for all administrative accounts; monitor Windows Event Logs for TOCTOU-related access patterns and privilege changes.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Race conditions occur when multiple concurrent requests exploit the brief time gap between checking a condition and acting upon it (TOCTOU - Time of Check, Time of Use).
Affected Products (CPE)CVE.org
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GitHub PoC
Exploit-DB