Quick answers
- Is CVE-2026-66305 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-66305 being exploited in the wild.
- How severe is CVE-2026-66305?
- High severity, with a CVSS score of 7.1, published 8 September 2026.
- Which products and versions are affected?
- Microsoft Skype for Business.
- Is there a fix for CVE-2026-66305?
- 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-2026-66305 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-66305?
- 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
The vulnerability exists in Skype for Business's implementation of client-side authentication, which fails to properly validate the origin and integrity of authentication credentials over the network. An authorized attacker with network access can intercept and replay authentication tokens or forge authentication claims to impersonate legitimate users. This is a spoofing vulnerability that requires network access but does not require prior compromise of user credentials. The attack vector is network-based and does not require local system access or user interaction beyond normal network communication.
Affected products
- Microsoft Skype for Business
Timeline
- 2026-09-08: disclosed