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PatchSiren cyber security CVE debrief

CVE-2026-66307 Microsoft CVE debrief

CVE-2026-66307 is an integer underflow vulnerability in Skype for Business that allows an unauthorized attacker to deny service over a network. The vulnerability has a CVSS score of 7.5 and is considered HIGH severity. Microsoft has released a patch for this vulnerability. Affected deployments should assess exposure and apply patches. The vulnerability is an integer underflow (wrap or wraparound) that could allow service denial. Evidence is based on official CVE and NVD records, which provide details on the vulnerability, including its description, CVSS score, and affected versions. However, specific version details and exploitability factors require verification.

Vendor
Microsoft
Product
Skype for Business Server 2015 CU13
CVSS
HIGH 7.5
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

Defenders responsible for Skype for Business Server deployments should assess exposure and apply patches. This includes reviewing inventory of affected deployments, verifying exposure, and applying Microsoft's patch. Security teams and vulnerability management teams should prioritize patching based on the HIGH severity and potential denial of service impact.

Why it matters

CVE-2026-66307 is an integer underflow vulnerability in Skype for Business that allows unauthorized attackers to potentially deny service. Defenders responsible for Skype for Business Server deployments should assess exposure and apply patches. The vulnerability has a CVSS score of 7.5 and is considered HIGH severity. Evidence is based on official CVE and NVD records.

  • Potential denial of service over a network
  • Requires verification of affected versions and exposure
  • Patch application is recommended

Technical summary

The vulnerability is an integer underflow (wrap or wraparound) in Skype for Business that allows an unauthorized attacker to deny service over a network. The CVSS vector is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. This vulnerability could allow attackers to potentially deny service. Affected product deployments require verification and patch application. The vulnerability has a CVSS score of 7.5 and is considered HIGH severity.

Defensive priority

Apply patches for Skype for Business Server

Recommended defensive actions

  • Apply patches for Skype for Business Server
  • Verify and apply Microsoft's patch
  • Review and update inventory of Skype for Business Server deployments

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and affected versions. Evidence is based on official CVE and NVD records. Specific version details and exploitability factors require verification. The vulnerability has a CVSS vector of CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Official records indicate a HIGH severity score of 7.5. Microsoft has released patches for affected Skype for Business Server deployments.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-66307 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-66307

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

  • CVE-2026-66307 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-66307

    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.