# CVE-2026-66307: Microsoft Skype for Business integer underflow denial of service

Source: https://junglewise.ai/threats/cve-2026-66307-microsoft-skype-for-business-integer-underflow-denial-of-service  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-08. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-66307 · Severity: high · CVSS 7.5 · Published 2026-09-08

Skype for Business, a widely-deployed enterprise communication platform, contains an integer underflow vulnerability that allows an attacker on the network to cause the service to crash or become unavailable. This vulnerability requires no user interaction or authentication, making it straightforward to exploit and potentially affecting an organization's communication capabilities.

Technologies: [Microsoft Skype for Business](https://junglewise.ai/threats/technologies/skype-for-business). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-66307 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-66307 being exploited in the wild.

**How severe is CVE-2026-66307?** High severity, with a CVSS score of 7.5, published 8 September 2026.

**Which products and versions are affected?** Microsoft Skype for Business.

**Is there a fix for CVE-2026-66307?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-66307 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-66307?** Check whether you run Microsoft Skype for Business. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An integer underflow (wrap or wraparound) vulnerability exists in Skype for Business that allows an unauthenticated attacker to send specially crafted network packets to trigger a denial of service condition. The vulnerability is remotely exploitable over the network without requiring authentication or user interaction. Successful exploitation causes service disruption, preventing users from accessing Skype for Business functionality. The attack vector is network-based, making it a significant concern for internet-facing deployments or those within corporate networks.

## Affected products

- Microsoft Skype for Business

## Timeline

- 2026-09-08: disclosed

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66307](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66307)

## Related threats

- [Microsoft Skype for Business and Lync privilege escalation](https://junglewise.ai/threats/cve-2026-85873-improper-authorization-in-skype-for-business-and-microsoft-lync)
- [Microsoft Skype for Business cryptographic signature spoofing](https://junglewise.ai/threats/cve-2026-69646-microsoft-skype-for-business-cryptographic-signature-spoofing)
- [Microsoft Skype for Business cross-site scripting in web page generation](https://junglewise.ai/threats/cve-2026-69642-microsoft-skype-for-business-cross-site-scripting-in-web-page)
- [Microsoft Skype for Business out-of-bounds read](https://junglewise.ai/threats/cve-2026-66308-microsoft-skype-for-business-out-of-bounds-read)
- [Microsoft Skype for Business information disclosure in error messages](https://junglewise.ai/threats/cve-2026-66306-microsoft-skype-for-business-information-disclosure-in-error)