How severe is CVE-2026-55040?

CVE-2026-55040 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-55040 being actively exploited?

Yes. CVE-2026-55040 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2026-08-18, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2026-55040?

CVE-2026-55040 primarily affects Microsoft Sharepoint Server. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-55040?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

When was CVE-2026-55040 published?

CVE-2026-55040 was published on 2026-07-14 and last updated on 2026-08-19.

CVE-2026-55040

CVE-2026-55040 is a critical-severity vulnerability in Microsoft Sharepoint Server with a CVSS 3.x base score of 9.1. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2026-08-18). The underlying weakness is classified as CWE-1390.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
EPSS exploit prediction: 5% (92nd percentile)
Actively exploited: Yes — listed in CISA KEV (added 2026-08-18)
Weakness: CWE-1390
Affected product: Microsoft Sharepoint Server
Published: 2026-07-14
Last modified: 2026-08-19

Description

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

Frequently asked questions

What is CVE-2026-55040?: Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
How severe is CVE-2026-55040?: CVE-2026-55040 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-55040 being actively exploited?: Yes. CVE-2026-55040 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2026-08-18, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2026-55040?: CVE-2026-55040 primarily affects Microsoft Sharepoint Server. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-55040?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
When was CVE-2026-55040 published?: CVE-2026-55040 was published on 2026-07-14 and last updated on 2026-08-19.

References

Affected products (3)

cpe:2.3:a:microsoft:sharepoint_server:*:*:*:*:subscription:*:*:*
cpe:2.3:a:microsoft:sharepoint_server:2016:*:*:*:enterprise:*:*:*
cpe:2.3:a:microsoft:sharepoint_server:2019:*:*:*:*:*:*:*

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