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Microsoft Security Response CenterCVE-2026-66307

Skype for Business and Lync Denial of Service Vulnerability

Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.

Read the vendor bulletin Get alerts for Skype for Business Server 2015 CU13
7.5CVSS out of 10High severity
Scope

What the vendor says is affected

  • Skype for Business Server 2015 CU13
  • Skype for Business Server Subscription Edition CU1
  • Skype for Business Server 2019 CU8

Versions the vendor lists as fixed

  • 6.0.9319.885
  • 7.0.2046.879
  • 7.0.2046.569
Next step

What the vendor recommends

Install KB5123301. Install KB5123287. Install KB5123300.

Review the complete instructions on the vendor's site
Timeline

When this advisory changed

  1. Published by Microsoft Security Response Center

    The publication date reported by the vendor.

  2. Added to SecurityAlert

    We collected the advisory from the official source.

  3. Confirmed at the source

    Our collector saw this advisory during a later source check.

Vulnerabilities

CVEs named in this advisory

CVE-2026-66307View CVSS, KEV, EPSS, and threat context
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