CVE-2026-66307 Skype for Business and Lync Denial of Service Vulnerability
An integer underflow in Skype for Business Server allows an unauthorized attacker to cause a denial of service over the network.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-66307?
CVE-2026-66307 is a high-severity vulnerability in Microsoft Skype for Business Server 2015 CU13, published on 8 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
Weakness: CWE-191
Which versions are affected by CVE-2026-66307?
It affects 2 products.
Products include Microsoft Skype for Business Server, Microsoft Skype for Business Server Subscription Edition.
How do I fix CVE-2026-66307?
No fix has been published for CVE-2026-66307 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-66307 being exploited?
There is no known exploitation of CVE-2026-66307 in the wild and no public exploit code.
Other vulnerabilities in Microsoft Skype for Business Server 2015 CU13
- CVE-2023-41763 Microsoft Skype for Business Privilege Escalation
- CVE-2026-66302 Skype for Business Remote Code Execution Vulnerability
- CVE-2026-69646 Skype for Business Spoofing Vulnerability
- CVE-2026-66304 Skype for Business Information Disclosure Vulnerability
- CVE-2023-36780 Skype for Business Remote Code Execution Vulnerability
Sources
Also known as GHSA-fmx2-865f-8c6j.