CVE-2026-66305: microsoft skype_for_business_server Use of Client-Side Authentication
CVSS: 7.1v3.1HighAnalyzed
Published 08-09-2026Last modified 14-10-2026
Vulnerability summary
CVE-2026-66305 is a high (CVSS 7.1) Use of Client-Side Authentication vulnerability in microsoft skype_for_business_server. EPSS estimates a 0.53% chance of exploitation in the next 30 days, higher than 43.4% of scored vulnerabilities.
CVSS score
7.1/10
010
High · v3.1 (CVE.org)EPSS score
0.53%
0%100%
Low · +0.23 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Timeline
- 08-09-2026PublishedVulnerability first disclosed.
- 14-10-2026Last modifiedVulnerability information updated.
Description
Use of client-side authentication in Skype for Business allows an authorized attacker to perform spoofing over a network.
CVSS metrics
2 scores · 2 sources · 1 versionHigh 7.1Preferred score · CVE.org (CNA)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N/E:U/RL:O/RC:CSourcesAll 2 agree
- NVDNIST7.1HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N
EPSS trend
Probability
0.53%
Chance of exploitation in the next 30 days
Percentile
43%
Versus all other CVEs
30-day change
+0.23 pp
From 0.30% on 20-09-2026
20-09-202620-10-2026
EPSS score0.53%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Microsoft5 products
- skype_for_business_server2015:cumulative_update_13 | 2015:cumulative_update_13_hotfix_2 | 2019:cumulative_update_8 | 2019:cumulative_update_8_hotfix1 | 2019:cumulative_update_8_hotfix2
- skype for business server 2015 cu13≥ 9319.0, < 6.0.9319.885
- skype for business server 2019 cu8≥ 2046.0, < 7.0.2046.569
- skype_for_business_server_subscription_edition7.0.2046.849
- skype for business server subscription edition cu1≥ 2046.0, < 7.0.2046.879
1 vendor · 5 products
