CVE-2026-66307: Skype for Business and Lync Denial of Service Vulnerability
Published Sep 8, 2026
·Updated
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
Other sources
Skype for Business and Lync Denial of Service Vulnerability
— Microsoft
Affected Software
9 affected componentsFixes available
Microsoft Skype for Business Server Subscription Edition CU1<7.0.2046.879
7.0.2046.879
Microsoft Skype for Business Server 2019 CU8<7.0.2046.569
7.0.2046.569
Microsoft Skype for Business Server 2015 CU13<6.0.9319.885
6.0.9319.885
Microsoft Skype for Business Server=2015-cumulative_update_13
Microsoft Skype for Business Server=2015-cumulative_update_13_hotfix_2
Microsoft Skype for Business Server=2019-cumulative_update_8
Microsoft Skype for Business Server=2019-cumulative_update_8_hotfix1
Microsoft Skype for Business Server=2019-cumulative_update_8_hotfix2
Microsoft Skype For Business Server Subscription Edition=7.0.2046.849
Remediation
Event History
Sep 8, 2026
CVE Published
via Microsoft·02:00 PM
Data Sourced
via Microsoft·02:00 PM
DescriptionSeverityWeaknessAffected Software
CVE Published
via MITRE·06:39 PM
Data Sourced
via MITRE·06:39 PM
DescriptionSeverity
Data Sourced
via NVD·07:18 PM
RemedyDescriptionSeverityWeaknessAffected Software
Frequently Asked Questions
1
Which deployments are affected?
Affected products are Microsoft Skype for Business Server Subscription Edition CU1, Skype for Business Server 2019 CU8, and Skype for Business Server 2015 CU13.
2
Does exploitation require authentication or user interaction?
No. The vulnerability is network-accessible and the supplied vector indicates that an attacker does not need privileges or user interaction.
3
What is the expected impact of exploitation?
Successful exploitation can allow an unauthorized attacker to cause a denial of service. The supplied impact metrics indicate availability impact only, with no stated confidentiality or integrity impact.