Authenticated spoofing via client-side authentication
Published Sep 8, 2026 · Updated Sep 10, 2026
Client-side authentication in Microsoft Skype for Business Server allows remote authenticated users to spoof identities over a network. Microsoft identifies the flaw as client-side authentication but does not disclose the affected component or validation logic. A valid account is required; exploitation can impersonate another party and undermine communication authenticity, with limited information exposure and no reported service interruption.
Summary
What happened
Client-side authentication in Microsoft Skype for Business Server allows remote authenticated users to spoof identities over a network. Microsoft identifies the flaw as client-side authentication but does not disclose the affected component or validation logic. A valid account is required; exploitation can impersonate another party and undermine communication authenticity, with limited information exposure and no reported service interruption.
The record
- CVE
- CVE-2026-66305
- Published
- Sep 8, 2026
- Updated
- Sep 10, 2026
- Vendor
- Microsoft
- Product
- Skype for Business Server Subscription Edition
- Classifications
- CWE-603
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 8, 2026CVE publishedPublication date reported by the CVE source.
- Sep 10, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=2046.0 <7.0.2046.879
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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