CVE-2026-66305 Skype for Business Spoofing Vulnerability
An authorized attacker can perform spoofing attacks due to client-side authentication flaws in Skype for Business Server.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-66305?
CVE-2026-66305 is a high-severity authentication bypass vulnerability in Microsoft Skype for Business Server 2015 CU13, published on 8 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Use of client-side authentication in Skype for Business allows an authorized attacker to perform spoofing over a network.
Weakness: CWE-603
Which versions are affected by CVE-2026-66305?
It affects 2 products.
Products include Microsoft Skype for Business Server, Microsoft Skype for Business Server Subscription Edition.
How do I fix CVE-2026-66305?
No fix has been published for CVE-2026-66305 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-66305 being exploited?
There is no known exploitation of CVE-2026-66305 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-2026-66307 Skype for Business and Lync Denial of Service Vulnerability
Sources
Also known as GHSA-9823-h4m8-w7cq.