CVE-2026-66307Important
Skype for Business and Lync Denial of Service Vulnerability
Assessment
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
- Severity
- Important
- CVSS base score
- 7.5CVSS:3.1/
AV:N/ AC:L/ PR:N/ UI:N/ S:U/ C:N/ I:N/ A:H/ E:U/ RL:O/ RC:C - Impact
- Denial of Service
- EPSS, next 30 days
- 1.2%Higher than 66.2% of scored CVEs · FIRST model run 26 Sep 2026 · about EPSS
- Exploitability
- Exploitation Less Likely
- Publicly disclosed
- No
- Customer action
- Required: apply the update
- Component
- Skype for Business
- Weakness
- CWE-191: Integer Underflow (Wrap or Wraparound)
- Issued by
- Microsoft
- Published
- 8 Sep 2026 · September 2026
- Last revised
- 8 Sep 2026
Updates that fix it
3 KBs| KB | Type | Restart | Applies to | Other CVEs |
|---|---|---|---|---|
| KB5123287 | Security Update | — | Skype for Business Server Subscription Edition CU1 | All CVEs in KB5123287 |
| KB5123300 | Security Update | — | Skype for Business Server 2019 CU8 | All CVEs in KB5123300 |
| KB5123301 | Security Update | — | Skype for Business Server 2015 CU13 | All CVEs in KB5123301 |
Affected products
Microsoft Office3 affected products
- Skype for Business Server 2015 CU13
- Skype for Business Server 2019 CU8
- Skype for Business Server Subscription Edition CU1