CVE-2026-21513
Microsoft Windows 10 21H2 ≤ 10.0.19044.6937
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HSummary
CVE-2026-21513 is a high-severity Protection Mechanism Failure (CWE-693) vulnerability in Microsoft Windows 10 21H2. Its CVSS base score is 8.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Abuse Elevation Control Mechanism (T1548); ranked in the top 4% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.
The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-21513 is a protection mechanism failure vulnerability in the MSHTML Framework, classified under CWE-693. This security feature bypass affects the MSHTML rendering engine, a component historically used in Microsoft Internet Explorer and legacy Edge browsers. Published on February 10, 2026, it carries a CVSS v3.1 base score of 8.8 (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H), indicating high severity due to its potential for significant impact on confidentiality, integrity, and availability.
An unauthorized attacker can exploit this vulnerability over a network with low complexity and no required privileges, though user interaction is necessary. By tricking a user into interacting with malicious content, such as via a crafted webpage or document, the attacker can bypass a security feature in MSHTML, potentially leading to arbitrary code execution or other high-impact compromises on the affected system.
Microsoft's update guide at msrc.microsoft.com provides details on patches and remediation. Vicarius offers specific detection and mitigation scripts tailored to this MSHTML security feature bypass. The vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, signaling active exploitation in the wild and urging immediate patching by federal agencies.
As a high-severity issue in a legacy but still-deployed component, CVE-2026-21513 underscores the risks of unpatched Microsoft browser engines, with confirmed real-world exploitation per CISA. Security practitioners should prioritize inventorying and updating affected systems.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-7342
Vulnerability Data
Protection mechanism failure in MSHTML Framework allows an unauthorized attacker to bypass a security feature over a network.
- CWE(s)
- KEV Date Added
- 10 February 2026
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 8 hardening rules · 6 OS baselines
V6.3.3V6.6.3V10.2.2
Mitigating Controls (NIST 800-53 r5) AI
AC-3 directly requires enforcement of access authorizations via the protection mechanism itself.
AC-4 mandates use of information flow enforcement mechanisms to control data movement.
SC-2 requires separation of user and system functionality as a protection mechanism.
SC-28 requires protection mechanisms for information at rest.
SC-3 requires isolation of security functions from non-security functions.
SC-7 requires boundary protection mechanisms to monitor and control external communications.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Enforcing authentication directly implements a core protection mechanism whose absence or misuse is the CWE.
Defining and enforcing access authorizations is a protection mechanism; proper use prevents the CWE.
Cryptographic and integrity controls are protection mechanisms whose correct deployment mitigates the CWE.
Encryption and integrity protections for transit are explicit protection mechanisms.
Logical network protections are protection mechanisms whose failure matches the CWE.
Hardened configuration baselines ensure protection mechanisms are correctly applied and maintained.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Systematic verification that security mechanisms operate according to defined standards reduces the likelihood that protection mechanisms are bypassed or disabled.
Hardening devices, disabling vulnerable protocols, and maintaining accurate network diagrams reduce the likelihood that a protection mechanism is misconfigured or left in a weak state.
Requiring defined escalation paths, crisis activation criteria, and coordination procedures strengthens the overall protection mechanism so that a single control failure is less likely to leave the organization exposed.
By requiring a documented categorization and decision process for security events, the control ensures that protection mechanisms are not bypassed or ignored when anomalies occur.
Identifying and remediating control weaknesses that contributed to an incident reduces the likelihood that protection mechanisms will fail again.
Post-incident analysis that feeds updated risk assessments and additional controls directly reduces the chance that previously exploited weaknesses will recur.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (2 rules)
- V-248524 OL 8 must implement NIST FIPS-validated cryptography for the following: To provision digital signatures, to generate cryptographic hashes, and to protect data requiring data-at-rest protections in accordance with applicable federal laws, Executive Orders, directives, policies, regulations, and standards. prevents CWE-693
- V-248525 All OL 8 local disk partitions must implement cryptographic mechanisms to prevent unauthorized disclosure or modification of all information that requires at-rest protection. prevents CWE-693
Windows 10 (2 rules)
- V-220865 The Windows Remote Management (WinRM) service must not use Basic authentication. prevents CWE-693
- V-220812 Credential Guard must be running on Windows 10 domain-joined systems. prevents CWE-693
Windows 11 (1 rule)
- V-253418 The Windows Remote Management (WinRM) service must not use Basic authentication. prevents CWE-693
Windows Server 2016 (1 rule)
- V-225012 Windows Server 2016 must be running Credential Guard on domain-joined member servers. prevents CWE-693
Windows Server 2019 (1 rule)
- V-205907 Windows Server 2019 must be running Credential Guard on domain-joined member servers. prevents CWE-693
Windows Server 2022 (1 rule)
- V-254441 Windows Server 2022 must be running Credential Guard on domain-joined member servers. prevents CWE-693