CVE-2026-55040: Microsoft SharePoint weak authentication security feature bypass

CVE-2026-55040 · Severity: critical · CVSS 9.1 · Exploited in the wild · Published 2026-07-14

Microsoft SharePoint is a widely-deployed collaboration and document management platform used by many organizations. This authentication weakness allows attackers to gain unauthorized access to SharePoint instances over the network without valid credentials, potentially exposing sensitive business documents, customer data, and internal communications. Active exploitation has been observed in the wild.

Technologies: Microsoft SharePoint, Microsoft SharePoint Enterprise Server 2016, Microsoft SharePoint Server 2019, Microsoft SharePoint Server Subscription Edition. Vendors: Microsoft.

Quick answers

Is CVE-2026-55040 exploited in the wild?
Yes. CVE-2026-55040 is known to be exploited in the wild, first recorded on 18 August 2026. Treat it as urgent.
How severe is CVE-2026-55040?
Critical severity, with a CVSS score of 9.1, published 14 July 2026.
Which products and versions are affected?
Microsoft SharePoint Enterprise Server 2016 < 16.0.5561.1001; Microsoft SharePoint Server 2019 < 16.0.10417.20175; Microsoft SharePoint Server Subscription Edition < 16.0.19725.20434.
Is there a fix for CVE-2026-55040?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-55040 attacked?
It is attacked over the network.
Am I affected by CVE-2026-55040?
Check whether you run Microsoft SharePoint, Microsoft SharePoint Enterprise Server 2016, Microsoft SharePoint Server 2019 or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

This vulnerability is an authentication bypass in Microsoft SharePoint that allows unauthorized access over the network without proper credential validation. The weak authentication mechanism enables attackers to circumvent security controls and gain access to the SharePoint environment. The vulnerability is network-reachable and does not require prior authentication or user interaction to exploit. An attacker can leverage this flaw to access sensitive data, modify content, or establish persistence within the SharePoint infrastructure. The vulnerability has been actively exploited in the wild as of the publication date.

Affected products

  • Microsoft SharePoint

Timeline

  • 2026-08-18: disclosed
  • 2026-08-18: exploited

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