Microsoft Security Update Guide · Skype for Business
Skype for Business Spoofing Vulnerability
Published
What does this mean?
- Spoofing. An attacker can pretend to be another user or source, for example through a misleading link or page.
- It can be exploited over the network (including from the internet if the service is reachable there), with an ordinary user account and without any user action.
- CVSS 7.1 out of 10: high. Microsoft rates it Important.
- No attacks reported; Microsoft expects exploitation to be less likely.
- What should you do? Install the security update for the version you run (or a later cumulative update):
- Skype for Business Server 2019 CU8: KB5123300
7.0.2046.569 - Skype for Business Server 2015 CU13: KB5123301
6.0.9319.885 - Skype for Business Server Subscription Edition CU1: KB5123287
7.0.2046.879
- Skype for Business Server 2019 CU8: KB5123300
Use of client-side authentication in Skype for Business allows an authorized attacker to perform spoofing over a network.
Key facts
Released
8 sep 2026
Impact
Spoofing
Max severity
Important
Weakness
CVSS 3.1
7.1 / 6.2 (base / temporal)
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N/E:U/RL:O/RC:CPublicly disclosed
No
Exploited
No
Exploitability assessment
Exploitation Less Likely
Customer action required
Yes
Links
CVSS metrics
| Base score metrics | |
|---|---|
| Attack Vector | Network |
| Attack Complexity | Low |
| Privileges Required | Low |
| User Interaction | None |
| Scope | Unchanged |
| Confidentiality | Low |
| Integrity | High |
| Availability | None |
| Temporal score metrics | |
| Exploit Code Maturity | Unproven |
| Remediation Level | Official Fix |
| Report Confidence | Confirmed |
Affected products and updates
| Product | Update | Build |
|---|---|---|
| Skype for Business Server 2019 CU8 | KB5123300 | 7.0.2046.569 |
| Skype for Business Server 2015 CU13 | KB5123301 | 6.0.9319.885 |
| Skype for Business Server Subscription Edition CU1 | KB5123287 · Security Update | 7.0.2046.879 |
FAQ
- According to the CVSS metric, successful exploitation of this vulnerability could lead to a total loss of integrity (I:H). What does that mean for this vulnerability?
- An attacker who successfully exploited this vulnerability could inject content that appears to come from a trusted source, causing the affected application to display spoofed or manipulated content to the user.
Revisions
| Version | Date | Note |
|---|---|---|
| 1 | 8 sep 2026 | Information published. |
This is in the weekly digest for week 37 · What changed this week? →
View at Microsoft → ← All security advisories
Source: Microsoft Security Update Guide. 365Fanatic is not affiliated with Microsoft.
