Microsoft SharePoint Server Missing Authentication for Critical Function
CVE-2026-56164 is a critical-severity missing authentication for critical functionality vulnerability in Microsoft SharePoint Enterprise Server 2016 from Microsoft, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 16.0.5561.1001 as the first without the flaw, so updating Microsoft SharePoint Enterprise Server 2016 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on July 14, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Microsoft SharePoint Enterprise Server 2016 to 16.0.5561.1001 or a later version.
- Update Microsoft SharePoint Server 2019 to 16.0.10417.20175 or a later version.
- Update Microsoft SharePoint Server Subscription Edition to 16.0.19725.20434 or a later version.
- CISA's required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Microsoft SharePoint Enterprise Server 2016 | 16.0.0 up to, but not including, 16.0.5561.1001 | 16.0.5561.1001 |
| Microsoft | Microsoft SharePoint Server 2019 | 16.0.0 up to, but not including, 16.0.10417.20175 | 16.0.10417.20175 |
| Microsoft | Microsoft SharePoint Server Subscription Edition | 16.0.0 up to, but not including, 16.0.19725.20434 | 16.0.19725.20434 |
| Microsoft | Sharepoint Server | before 16.0.19725.20434; 2016; 2019 | 16.0.19725.20434 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 5.3 | Medium | CNA (microsoft.com) |
| CVSS 3.1 | 9.8 | Critical | NVD |
Official description
Missing authentication for critical function in Microsoft Office SharePoint allows an unauthorized attacker to elevate privileges over a network.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Missing Authentication for Critical Functionality
The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.
How developers prevent this class of flaw
- For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using libraries with authentication capabilities such as OpenSSL or the ESAPI Authenticator.
- When storing data in the cloud (e.g., S3 buckets, Azure blobs, Google Cloud Storage, etc.), use the provider's controls to require strong authentication for users who should be allowed to access the data.
More Missing Authentication for Critical Functionality vulnerabilities (CWE-306)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: partial).
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
References
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-56164US Government Resource
Other vulnerabilities in Microsoft SharePoint Enterprise Server 2016
- 9.3 Critical severity
- 8.8 High severity
Microsoft SharePoint Code Injection Exploited
Recent Missing Authentication for Critical Functionality vulnerabilities
- 9.3 Critical severity
- 7.3 High severity
- 8.6 High severity
- 7.8 High severity
- 10.0 Critical severity
- 9.8 Critical severity
Spotted an error? Tell us.