Evidence used
- No CISA KEV confirmation is currently recorded.
- The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
- EPSS is 1.33% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-23666High confidence
.NET Framework Denial of Service Vulnerability
Microsoft · Microsoft .NET Framework 3.5
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 Microsoft .NET Framework 3.5 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
A flaw was found in .NET Framework. An unauthorized attacker can exploit a race condition, which is a concurrent execution using shared resources with improper synchronization, to deny service over a network. This vulnerability can lead to a Denial of Service (DoS) for affected systems.
What
A flaw was found in .NET Framework. An unauthorized attacker can exploit a race condition, which is a concurrent execution using shared resources with improper synchronization, to deny service over a network. This vulnerability can lead to a Denial of Service (DoS) for affected systems.
Why
If two threads of execution use a resource simultaneously, there exists the possibility that resources may be used while invalid, in turn making the state of execution undefined.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
What
A flaw was found in .NET Framework. An unauthorized attacker can exploit a race condition, which is a concurrent execution using shared resources with improper synchronization, to deny service over a network. This vulnerability can lead to a Denial of Service (DoS) for affected systems.
Why
If two threads of execution use a resource simultaneously, there exists the possibility that resources may be used while invalid, in turn making the state of execution undefined.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
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 → Race Condition within a Thread → disrupt the affected service
- Attack surface
- Network
- Privileges required
- None: unauthenticated exploitation is possible
- 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-366 ↗
CWE-366: Race Condition within a Thread. If two threads of execution use a resource simultaneously, there exists the possibility that resources may be used while invalid, in turn making the state of execution undefined.
- 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:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/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.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.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
- Microsoft .NET Framework 3.5: 3.5.0 < 2.0.50727.8982 & 3.0.30729.8976
- Microsoft .NET Framework 3.5 AND 4.7.2: 4.7.0 < 2.0.50727.9068 & 3.0.30729.9065 & 4.7.4141.0
- Microsoft .NET Framework 3.5 AND 4.8: 4.8.0 < 2.0.50727.9068 & 3.0.30729.9065 & 4.8.4801.0
- Microsoft .NET Framework 3.5 AND 4.8.1: 4.8.1 < 2.0.50727.9181 & 3.0.30729.9165 & 4.8.9332.0
- Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2: 4.7.0 < 4.8.4801.0
- Microsoft .NET Framework 4.8: 4.8.0 < 4.8.4801.0
- 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 14 Apr 2026 · Last source change 25 Sept 2026, 17:25 UTC · CWE-366 · Race Condition within a Thread
CVE recordCVE.org · 5.2
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-2026-22363
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceOther authority
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
- Vendor guidanceAuthoritative vendor guidance changed: removed remediation: acn.gov.it/aggiornamenti-mensili-microsoft-19.secure@microsoft.com ↗
- Before
- remediation: acn.gov.it/aggiornamenti-mensili-microsoft-19 · vendor advisory: msrc.microsoft.com/CVE-2026-23666
- After
- vendor advisory: msrc.microsoft.com/CVE-2026-23666
- Affected versionsThe structured affected or fixed version information changed.CNA ↗
- Before
- 3.5.0 < 2.0.50727.8982 & 3.0.30729.8976; 4.7.0 < 2.0.50727.9068 & 3.0.30729.9065 & 4.7.4141.0; 4.8.0 < 2.0.50727.9068 & 3.0.30729.9065 & 4.8.4801.0; 4.8.1 < 2.0.50727.9181 & 3.0.30729.9165 & 4.8.9332.0; 4.7.0 < 4.8.4801.0; 4.8.0 < 4.8.4801.0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
- After
- Microsoft .NET Framework 3.5: 3.5.0 < 2.0.50727.8982 & 3.0.30729.8976; Microsoft .NET Framework 3.5 AND 4.7.2: 4.7.0 < 2.0.50727.9068 & 3.0.30729.9065 & 4.7.4141.0; Microsoft .NET Framework 3.5 AND 4.8: 4.8.0 < 2.0.50727.9068 & 3.0.30729.9065 & 4.8.4801.0; Microsoft .NET Framework 3.5 AND 4.8.1: 4.8.1 < 2.0.50727.9181 & 3.0.30729.9165 & 4.8.9332.0; Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2: 4.7.0 < 4.8.4801.0; Microsoft .NET Framework 4.8: 4.8.0 < 4.8.4801.0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
- Remediation statusRemediation status changed from Mitigation available to Awaiting fix.secure@microsoft.com ↗
- Before
- Mitigation available
- After
- Awaiting fix
- Remediation statusRemediation status changed from Awaiting fix to Mitigation available.CSIRT Italia ↗
- Before
- Awaiting fix
- After
- Mitigation available
CVE published
Remediation guidance 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.