Missing Authentication in Microsoft SharePoint Server Allows Privilege Escalation
CISA: Microsoft SharePoint Server Missing Authentication for Critical Function Vulnerability
CVSS 3.1
9.8critical
EPSS
27%p98
Published
()
KEV added
AI analysis
Microsoft SharePoint Server contains a missing authentication for critical function vulnerability (CWE-306) that lets an unauthenticated attacker elevate privileges over a network without valid credentials. The flaw is triggered when the affected SharePoint function is accessed remotely without any authentication check, allowing an attacker to gain higher privileges than intended. Successful exploitation could enable an attacker to take elevated actions within the SharePoint environment, potentially leading to further compromise of the server and its data. All organizations running on-premises Microsoft SharePoint Server are potentially affected, though specific versions have not yet been enumerated by Microsoft or CISA. The vulnerability was added to CISA's Known Exploited Vulnerabilities catalog on 2026-07-14, indicating it is being actively exploited, and its EPSS score of 26.6% (98th percentile) reflects a high near-term exploitation risk.
What to do: Apply Microsoft's security updates for SharePoint Server as soon as they are available, and check Microsoft's advisory for the specific affected version ranges once published. In the meantime, restrict network access to SharePoint servers, especially for internet-facing instances, and verify whether your environment falls under CISA BOD 26-04 requirements given the KEV listing. Monitor for updated guidance from Microsoft and CISA, as exploitation is confirmed and patching urgency is high.
Affected
Microsoft SharePoint Server
—
Estimated exposure
masspotentially millions of users and well over 100,000 exposed installations worldwide — SharePoint Server is deployed across a massive enterprise and government installed base globally, and with no version restrictions yet published the plausible exposure spans the full on-premises SharePoint footprint.
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
Description
Missing authentication for critical function in Microsoft Office SharePoint allows an unauthorized attacker to elevate privileges over a network.
CISA Known Exploited Vulnerability
Affected
Microsoft SharePoint Server
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.
WatchTowr observed active exploitation of SharePoint RCE CVE-2026-50522 (CVSS 9.8), part of an ongoing wave of exploited on-prem SharePoint flaws patched by Microsoft.
On 14 July 2026 Microsoft released updates for critical SharePoint Server RCE flaws, including CVE-2026-50522 (CVSS 9.8), a deserialisation vulnerability possibly exploitable without authentication. On 20 July 2026 WatchTowr published PoC exploit code and observed active exploitation of CVE-2026-50522, prompting CISA to urge SharePoint hardening. The advisory also covers recently fixed SharePoint flaws: CVE-2026-32201 (6.5, spoofing), CVE-2026-45659 (8.8, authenticated RCE), CVE-2026-56164 (9.8, unauthenticated privilege escalation), and CVE-2026-58644 (9.8, unauthenticated RCE). Affected products include SharePoint Server Subscription Edition, 2019, and Enterprise Server 2016; CERT-EU recommends immediate patching, credential rotation, and compromise assessments.
Attackers exploit SharePoint authentication bypass CVE-2026-55040 (CVSS 9.1) after Rapid7's PoC release, with 12 exploitation attempts recorded since July 19, 2026.
Microsoft patched CVE-2026-55040 in its July 2026 Patch Tuesday; the 9.1-severity flaw chains four weaknesses in SharePoint's JWT token validation pipeline, letting unauthenticated attackers forge valid JWTs and impersonate any SharePoint site user or administrator. Threat actors began exploiting the bug after Rapid7 released a Python PoC that forges tokens and enumerates domain users by SID. KEVIntel telemetry shows 12 exploitation attempts since July 19, 2026, eight of them on August 12-13 following the PoC release, originating from eight IPs across Hong Kong, Japan, the Netherlands, Taiwan, and the U.S. This is the fifth SharePoint vulnerability exploited this year, alongside CVE-2026-45659, CVE-2026-56164, CVE-2026-58644, and CVE-2026-50522.