CVE-2026-66305
Undergoing Analysis Undergoing Analysis - In Progress

Spoofing via Client-Side Authentication in Skype for Business

Publication date: 2026-09-08

Last updated on: 2026-09-09

Assigner: Microsoft Corporation

Description
Use of client-side authentication in Skype for Business allows an authorized attacker to perform spoofing over a network.

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Meta Information

Published
2026-09-08
Last Modified
2026-09-09
Generated
2026-09-29
AI Q&A
2026-09-09
EPSS Evaluated
2026-09-27
NVD
CVE-2026-66305

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
microsoft skype_for_business *

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-603 A client/server product performs authentication within client code but not in server code, allowing server-side authentication to be bypassed via a modified client that omits the authentication check.

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Executive Summary

This vulnerability involves the use of client-side authentication in Skype for Business. An authorized attacker can exploit this to perform spoofing over a network, potentially impersonating legitimate users or systems.

Impact Analysis

An attacker could impersonate a user or system to gain unauthorized access, intercept communications, or perform actions on behalf of the victim. This could lead to data breaches, unauthorized transactions, or reputational damage.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Organizations may face fines, legal penalties, and loss of trust due to non-compliance.

Mitigation Strategies

Update Skype for Business to the latest version to address client-side authentication issues. Monitor network traffic for unusual authentication patterns or spoofing attempts. Restrict user permissions to minimize potential impact.

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