MSRC-CVE-2026-66305 — Skype for Business Spoofing Vulnerability

Summary

Impact: Spoofing. Microsoft rating: Important. Not known to be exploited — Exploitation Less Likely. Customer action: Required.

Details

According to the CVSS metric, successful exploitation of this vulnerability could lead to a total loss of integrity (I:H). What does that mean for this vulnerability?
An attacker who successfully exploited this vulnerability could inject content that appears to come from a trusted source, causing the affected application to display spoofed or manipulated content to the user.

Security updates
6.0.9319.885 — https://support.microsoft.com/help/5123301
7.0.2046.569 — https://support.microsoft.com/help/5123300
7.0.2046.879 — https://support.microsoft.com/help/5123287

Vulnerabilities 1

High 7.1

CVE-2026-66305

Skype for Business Spoofing Vulnerability

Use of client-side authentication in Skype for Business allows an authorized attacker to perform spoofing over a network.

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

Sep 8, 2026

Revision history

2026-09-08 #1
Information published.

References

CVE-2026-66305 Skype for Business Spoofing Vulnerability - HTML
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66305
Microsoft Exploitability Index
https://www.microsoft.com/en-us/msrc/exploitability-index?rtc=1
Microsoft Support Lifecycle
https://support.microsoft.com/lifecycle
Common Vulnerability Scoring System
https://www.first.org/cvss