CVE tracker / CVE-2026-66307

CVE-2026-66307

CVE-2026-66307 is the Skype for Business and Lync Denial of Service Vulnerability. Microsoft rates it Important, CVSS 7.5. It is not in CISA's Known Exploited Vulnerabilities catalog. Published September 8, 2026.

Risk summary

HighDenial of Service
7.5
CVSS v3 base
1.2%
EPSS: chance of exploitation in 30 days
High
Severity
Important
Microsoft's rating
Less Likely
Microsoft: exploitation
No
In CISA KEV

Microsoft describes it: “Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.”

How to fix it

Microsoft lists 3 affected products and the update that fixes each:

What Microsoft changed

Details

Weakness
CWE-191: Integer Underflow (Wrap or Wraparound)
Publicly disclosed (Microsoft)
No
Exploited (Microsoft)
No
Known exploited (CISA KEV)
Not listed
Published
September 8, 2026
Last revised
September 8, 2026

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References

Microsoft Security Update Guide NVD CVE record CWE

From Microsoft, CISA, NVD and FIRST data; the Microsoft details were read when this page was opened. Check the references above before you act.