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CVE-2026-66303 Microsoft CVE debrief

A null pointer dereference vulnerability in Skype for Business allows an authorized attacker to deny service over a network. This CVE was published on 2026-09-08T19:18:07.820Z and was last modified on 2026-09-16T19:23:02.977Z. The vulnerability has a CVSS score of 6.5 and a severity of MEDIUM. Skype for Business Server administrators and defenders should assess exposure and prioritize patching and verification efforts to prevent potential denial-of-service impacts. The CVE record and NVD entry provide details on the null pointer dereference vulnerability in Skype for Business Server. Microsoft has provided a patch and vendor advisory for this vulnerability.

Vendor
Microsoft
Product
Skype for Business Server 2015 CU13
CVSS
MEDIUM 6.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-08
Original CVE updated
2026-09-16
Advisory published
2026-09-08
Advisory updated
2026-09-16

Who should care

Skype for Business Server administrators and defenders should assess exposure and prioritize patching and verification efforts to prevent potential denial-of-service impacts. Additionally, security teams and vulnerability management teams should review the CVE record and NVD entry to understand the vulnerability and its potential impacts on their organization. Operators of affected systems should verify their systems

Why it matters

CVE-2026-66303 is a medium-severity vulnerability in Skype for Business Server that allows an authorized attacker to deny service over a network. Defenders should prioritize patching and verification efforts to prevent potential denial-of-service impacts.

  • Potential denial-of-service impact on Skype for Business Server deployments
  • Need for verification of affected versions and patch application
  • Potential impact on availability of Skype for Business Server services

Technical summary

The CVE record describes a null pointer dereference vulnerability in Skype for Business Server, which allows an authorized attacker to deny service over a network. The vulnerability has a CVSS score of 6.5 and a severity of MEDIUM. This vulnerability affects Skype for Business Server deployments, and defenders should prioritize patching and verification efforts to prevent potential denial-of-service impacts. The vulnerability can be exploited by an authorized attacker, and Microsoft has provided a patch and vendor advisory for this vulnerability.

Defensive priority

Medium-priority patching and verification recommended for Skype for Business Server deployments.

Recommended defensive actions

  • Apply the Microsoft patch for CVE-2026-66303
  • Verify Skype for Business Server deployments for potential exposure
  • Monitor for potential denial-of-service attempts

Evidence notes

The CVE record and NVD entry provide details on the null pointer dereference vulnerability in Skype for Business Server. Microsoft has provided a patch and vendor advisory for this vulnerability.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-66303 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-66303

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

  • CVE-2026-66303 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-66303

    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.