CVE-2026-56164: Microsoft SharePoint Server Missing Authentication for Critical Function Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on , the same day the CVE record was published.
- How likely is exploitation in the next 30 days?
- 1%
EPSS score, percentile 63.1 of all scored records
- How severe?
- 5.3 Medium
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA deadline . Apply mitigations in accordance with vendor instructions … Full text
- Which versions are affected?
Affected
- from 16.0.0 to before 16.0.5561.1001
- from 16.0.0 to before 16.0.10417.20175
- from 16.0.0 to before 16.0.19725.20434
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
What to do
Required action, set by CISA
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.
CISA due date for this action: .
Advisories and patches
Linked from CISA's catalog entry
- https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-56164
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- https://nvd.nist.gov/vuln/detail/CVE-2026-56164
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | from 16.0.0 to before 16.0.5561.1001 |
| Status | Versions |
|---|---|
| Affected | from 16.0.0 to before 16.0.10417.20175 |
| Status | Versions |
|---|---|
| Affected | from 16.0.0 to before 16.0.19725.20434 |
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
About this vulnerability
Microsoft SharePoint contains a missing authentication for critical function vulnerability that allows an unauthorized attacker to elevate privileges over a network.
Summary: CISA's KEV catalog, as of .
- CISA added CVE-2026-56164 to its Known Exploited Vulnerabilities (KEV) catalog on 14 Jul 2026.
- CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
- The due date CISA sets for the required action is 17 Jul 2026.
- The CVE record was published on 14 Jul 2026, the same day it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 5.3 (Medium), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 1% (percentile 63.1), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact partial.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of . About the data.
Description
Microsoft SharePoint Server Elevation of Privilege Vulnerability
Missing authentication for critical function in Microsoft Office SharePoint allows an unauthorized attacker to elevate privileges over a network.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
Weakness
- CWE-306: Missing Authentication for Critical Function
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| CVE record published | |
| Added to CISA KEV | |
| CISA due date for the required action | |
| CVE record last updated |
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