High severity · published Sep 8, 2026
CVE-2026-66307
Skype for Business and Lync Denial of Service Vulnerability
7.5
CVSS
1.2%
EPSS
No
On KEV
Description
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.2% · higher than 67% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SF
Skype for Business Server 2015 CU13 · Microsoft
9319.0 before 6.0.9319.885 · source: vendor
SF
Skype for Business Server 2019 CU8 · Microsoft
2046.0 before 7.0.2046.569 · source: vendor
SF
Skype for Business Server Subscription Edition CU1 · Microsoft
2046.0 before 7.0.2046.879 · source: vendor
SF
Skype For Business Server · Microsoft
2015; 2015; 2019; 2019; 2019 · source: NVD
SF
Skype For Business Server Subscription Edition · Microsoft
7.0.2046.849 · source: NVD
Affected product
SF
Skype for Business Server 2015 CU13
Microsoft
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-66307
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-66307
vendor-advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66307
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