CVE-2026-55040
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Critical
Known exploited
- Severity
- 9.1 / 10
- Critical · CVSS 3.1
- Exploit chance (EPSS)
- 69.54%
- Chance of exploitation in the next 30 days. Higher than 99.36% of scored vulnerabilities.
- Known exploited
- Yes
- In CISA's catalog since Aug 18, 2026
- Weakness
- CWE-1390 Weak Authentication
- Fix
- None yet
- No fixed version published
Exploited in the wild. Microsoft SharePoint Weak Authentication Vulnerability (Microsoft SharePoint). 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. Due for U.S. federal agencies by Aug 21, 2026.
Description
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
How to fix
No fixed version has been published yet. Until one is, remove or replace the package, or turn off or isolate the affected feature. This page updates when a fix ships.
Severity breakdown
CVSS 3.1 9.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
Weakness
CWE-1390: Weak Authentication
The product uses an authentication mechanism to restrict access to specific users or identities, but the mechanism does not sufficiently prove that the claimed identity is correct.
References
Advisories
Exploits and evidence
Other links
Timeline
- Published
- Added to CISA's Known Exploited Vulnerabilities catalog
- Last updated by the source
- Remediation due for U.S. federal agencies
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-qxvm-r42f-5p8j AVideo's Meet plugin: `uploadRecordedVideo.json.php` derives `users_id` from the uploaded filename and calls passwordless `User->login()`, allowing any caller with the Meet shared secret to obtain a session as arbitrary users including admin | Critical | Same weakness, CWE-1390 |
| GHSA-2865-hh9g-w894 Microsoft Security Advisory CVE-2025-24070: .NET Elevation of Privilege Vulnerability | High | Same weakness, CWE-1390 |
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