CVE-2026-66307
Skype for Business and Lync Denial of Service Vulnerability
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Exploit likelihood
What each source reports
CVE List Score used
Skype for Business and Lync Denial of Service Vulnerability
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
- Record
CVE-2026-66307- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C - Weakness
- CWE-191
- Updated
- 2026-11-02
EUVDEUVD-2026-73941
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
- Record
EUVD-2026-73941- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-fmx2-865f-8c6j
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to...
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
- Record
GHSA-fmx2-865f-8c6j- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Weakness
- CWE-191
- Updated
- 2026-11-02
NVD
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
- Record
CVE-2026-66307- CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Weakness
- CWE-191
- Updated
- 2026-11-02
Affected products
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-66307 is a high vulnerability (CVSS 7.5) in Microsoft Skype For Business Server 2015 Cu13, published September 8, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.17%, the 67th percentile. No source names a fixed version.