Cyber Resilience

CVE-2026-23666

Race Condition in Microsoft .Net Framework 3.5 … 4.8.1

Race Condition
Published
14 April 2026
Modified
15 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 7.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS Score 0.013 68th percentile
Risk Priority 60 floored blend · peak EPSS

Summary

CVE-2026-23666 is a high-severity Improper Handling of Exceptional Conditions (CWE-755) vulnerability in Microsoft .Net Framework. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 32% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SC-24 (Fail in Known State) — 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-2026-23666 is an improper input validation vulnerability in the .NET Framework that enables a denial-of-service condition. Published on 2026-04-14, it carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) and is associated with CWE-755 (Improper Handling of Exceptional Conditions). The flaw affects the .NET Framework component, allowing malformed inputs to trigger resource exhaustion or crashes.

An unauthorized attacker can exploit this vulnerability remotely over a network with low complexity and no user interaction required. By sending specially crafted inputs to a vulnerable .NET Framework application or service exposed to the network, the attacker can cause high-impact availability disruption, such as service crashes or excessive resource consumption, without affecting confidentiality or integrity.

The Microsoft Security Response Center (MSRC) provides an update guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23666, which details the vulnerability, affected versions, and recommended patches or mitigations for remediation.

OWASP Top 10 for Web (2025)

A10:2025 Mishandling of Exceptional Conditions

EU & UK References

Vulnerability Data

Improper input validation in .NET Framework allows an unauthorized attacker to deny service over a network.

CWE(s)
CWE-755CWE-366

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1489 Service Stop Impact
Adversaries may stop or disable services on a system to render those services unavailable to legitimate users.
attack.mitre.org →
T1499 Endpoint Denial of Service Impact
Adversaries may perform Endpoint Denial of Service (DoS) attacks to degrade or block the availability of services to users.
attack.mitre.org →
T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-20699Same product: Microsoft Windows 10 1809
CVE-2024-43636Same product: Microsoft Windows 10 1607
CVE-2024-43514Same product: Microsoft Windows 10 1607
CVE-2024-43623Same product: Microsoft Windows 10 1607
CVE-2024-43628Same product: Microsoft Windows 10 1607
CVE-2024-43635Same product: Microsoft Windows 10 1607
CVE-2024-43641Same product: Microsoft Windows 10 1607
CVE-2024-43646Same product: Microsoft Windows 10 1607
CVE-2024-38247Same product: Microsoft Windows 10 1607
CVE-2024-43627Same product: Microsoft Windows 10 1607

Affected Assets

microsoft
.net framework
3.5, 4.6.2, 4.7, 4.7.1, 4.7.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 1 hardening rule · 1 OS baseline
Validate
Prove the fix (OWASP ASVS)
  • V15.4.2
  • V15.4.3
  • V17.2.6

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can include concurrency and stress testing that finds race conditions after they have been coded.

SC-24 Fail in Known State good match

Requires the system to fail to a known safe state on specified failures, limiting the impact of unhandled exceptional conditions.

SI-17 Fail-safe Procedures good match

Mandates explicit fail-safe procedures triggered by indicated failures, structurally preventing unhandled or mishandled exceptional conditions.

SA-15 Development Process, Standards, and Tools partial match

Requiring documented development standards and tools can mandate use of safe concurrency patterns that avoid introducing races.

SA-8 Security and Privacy Engineering Principles partial match

Security engineering principles include requirements for synchronization primitives and thread-safe design that stop race conditions from being introduced.

SI-11 Error Handling partial match

Requires generation of appropriate error messages on exceptional conditions, directly enforcing correct handling rather than silent or incorrect behavior.

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.

PR.PS-06 mostly match
prevents

Secure SDLC practices explicitly require proper exception and error handling during design and coding.

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.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development and acceptance verifies correct handling of exceptional conditions.

A.5.37 Documented operating procedures partial match
degrades

Documented operating procedures may specify exception handling but do not guarantee implementation.

A.8.15 Logging partial match
finds

Logging captures unhandled exceptions, aiding detection but not preventing the weakness.

A.8.16 Monitoring activities partial match
finds

Monitoring can surface unhandled exceptions but does not enforce proper handling.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates exception-handling requirements and testing that directly prevent improper handling of exceptional conditions.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly include handling of error and exceptional conditions.

References