CVE-2026-66307: CWE-191: Integer Underflow (Wrap or Wraparound) in Microsoft Skype for Business Server 2015 CU13
Description
Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a network.
CVSS v3.1
Score 7.5high
Affected software
Microsoft
Skype for Business Server 2015 CU13
Microsoft
Skype for Business Server 2019 CU8
Microsoft
Skype for Business Server Subscription Edition CU1
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-66307) is classified as CWE-191 (Integer Underflow). It affects Microsoft Skype for Business Server 2015 CU13 versions within the ranges >=9319.0 <6.0.9319.885, >=2046.0 <7.0.2046.569, and >=2046.0 <7.0.2046.879. The integer underflow condition can be triggered remotely without privileges or user interaction, resulting in denial of service (DoS) by causing the service to crash or become unavailable. The vulnerability has a CVSS v3.1 base score of 7.5, indicating high severity. Microsoft has issued an official fix to address this vulnerability.
Potential Impact
An attacker can remotely cause a denial of service condition on affected Skype for Business Server 2015 CU13 instances by exploiting the integer underflow vulnerability. This impacts the availability of the service but does not affect confidentiality or integrity. There are no known exploits in the wild at this time.
Mitigation Recommendations
An official fix is available from Microsoft. Administrators should apply the security update provided in the Microsoft advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66307 to remediate this vulnerability. No additional mitigation steps are required beyond applying the patch.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- microsoft
- Date Reserved
- 2026-07-24T18:06:51.294Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- official-fix
- Vendor Advisory Urls
- [{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66307","vendor":"Microsoft"}]
Threat ID: 6aa059e1acd9273b4913b7f4
Added to database: 09/08/2026, 18:54:25 UTC
Last enriched: 10/14/2026, 21:29:42 UTC
Last updated: 10/23/2026, 15:10:14 UTC
Views: 84
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
External Links
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.