Microsoft Security Update Guide · SharePoint
Microsoft SharePoint Server Spoofing Vulnerability
Published · updated 21 sep 2026
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 6.5 out of 10: medium. 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):
- Microsoft SharePoint Server Subscription Edition: KB5002893
16.0.19725.20522 - Microsoft SharePoint Server 2019: KB5002894
16.0.10417.20198 - Microsoft SharePoint Server 2019: KB5002896
16.0.10417.20198 - Microsoft SharePoint Enterprise Server 2016: KB5002905
16.0.5565.1001 - Microsoft SharePoint Enterprise Server 2016: KB5002906
16.0.5565.1001
- Microsoft SharePoint Server Subscription Edition: KB5002893
- This applies to SharePoint Server you run yourself. Microsoft updates SharePoint Online in Microsoft 365.
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.
SharePoint Office / Microsoft 365 Apps
How do I check if I am affected?
SharePoint Server: check and update
- Check your farm build in the SharePoint Management Shell:
Or in Central Administration → Upgrade and Migration → Check product and patch installation status.(Get-SPFarm).BuildVersion - If the build is equal to or higher than the build under "Affected products and updates" below, this vulnerability is fixed. A later cumulative update includes the fix too.
- Otherwise install the update on every server in the farm, then run the SharePoint Products Configuration Wizard, or:
PSConfig.exe -cmd upgrade -inplace b2b -wait -cmd applicationcontent -install -cmd installfeatures -cmd secureresources -cmd services -install - You do not need to update SharePoint Online in Microsoft 365; Microsoft does that.
What kind of flaw is this?
- CWE-502: Deserialization of Untrusted Data
The software turns received data into objects without checking it. With crafted data an attacker can get code to run.
Key facts
Released
11 aug 2026
Last revised
21 sep 2026 (v1.1)
Impact
Spoofing
Max severity
Important
Weakness
CVSS 3.1
6.5 / 5.7 (base / temporal)
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/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 | High |
| Integrity | None |
| Availability | None |
| Temporal score metrics | |
| Exploit Code Maturity | Unproven |
| Remediation Level | Official Fix |
| Report Confidence | Confirmed |
Affected products and updates
| Product | Update | Build |
|---|---|---|
| Microsoft SharePoint Server Subscription Edition | KB5002893 · Security Update | 16.0.19725.20522 |
| Microsoft SharePoint Server 2019 | KB5002894 · Security Update | 16.0.10417.20198 |
| Microsoft SharePoint Server 2019 | KB5002896 · Security Update | 16.0.10417.20198 |
| Microsoft SharePoint Enterprise Server 2016 | KB5002905 · Security Update | 16.0.5565.1001 |
| Microsoft SharePoint Enterprise Server 2016 | KB5002906 · Security Update | 16.0.5565.1001 |
FAQ
- There are multiple update packages available for some of the affected software. Do I need to install all the updates listed in the Security Updates table for the software?
- Yes. Customers should apply all updates offered for the software installed on their systems. If multiple updates apply, they can be installed in any order.
- According to the CVSS metric, successful exploitation of this vulnerability could lead to loss of confidentiality (C:H)? What does that mean for this vulnerability?
- Successful exploitation of this vulnerability allows an attacker to impersonate another user and access information based on the victim user's permission levels.
- I am running SharePoint Server 2016. Do the updates for SharePoint Enterprise Server 2016 also apply to the version I am running?
- Yes. The same KB number applies to both SharePoint Server 2016 and SharePoint Enterprise Server 2016. Customers running either version should install the security update to be protected from this vulnerability.
Revisions
| Version | Date | Note |
|---|---|---|
| 1.1 | 21 sep 2026 | Updated an acknowledgement. This is an informational change only. |
| 1 | 11 aug 2026 | Information published. |
This is in the weekly digest for week 39 · What changed this week? →
View at Microsoft → ← All security advisories
Source: Microsoft Security Update Guide. 365Fanatic is not affiliated with Microsoft.
