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PatchSiren cyber security CVE debrief

CVE-2026-42904 Microsoft CVE debrief

CVE-2026-42904 is a critical vulnerability in Windows TCP/IP that allows an unauthorized attacker to elevate privileges over an adjacent network. The vulnerability has a CVSS score of 9.6 and is classified as CRITICAL.

Vendor
Microsoft
Product
Windows 10 Version 21H2
CVSS
CRITICAL 9.6
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-09
Original CVE updated
2026-06-11
Advisory published
2026-06-09
Advisory updated
2026-06-11

Who should care

Administrators and users of Windows 10, Windows 11, and Windows Server are advised to take immediate action to mitigate this vulnerability.

Technical summary

A heap-based buffer overflow vulnerability exists in Windows TCP/IP, which allows an unauthorized attacker to elevate privileges over an adjacent network. The vulnerability is caused by improper handling of TCP/IP packets, leading to a buffer overflow condition.

Defensive priority

High

Recommended defensive actions

  • Apply patches and updates from Microsoft as soon as possible.
  • Implement network segmentation and isolation to limit the attack surface.
  • Monitor network traffic for suspicious activity.

Evidence notes

The vulnerability is confirmed by Microsoft and has been analyzed by the National Vulnerability Database (NVD).

Sources and references

Verified primary and authoritative sources

  • CVE-2026-42904 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-42904

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-42904 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-42904

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.