CVE-2026-55040
CriticalExploitedPublic exploitWeak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Published Jul 14, 2026 · Updated Oct 8, 2026
Key Facts
Patch immediately- CVE-2026-55040 is a critical-severity vulnerability (CVSS 9.1 v3.1) affecting Sharepoint Server (Microsoft), Sharepoint Server 2016 (Microsoft), Sharepoint Server 2019 (Microsoft) and 2 more products.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Aug 12, 2026. Public exploit code is available.
- EPSS estimates a 70% probability of exploitation in the next 30 days.
- Fixed versions are available, including Microsoft SharePoint Enterprise Server 2016 16.0.5561.1001, Sharepoint Server 16.0.19725.20434, Sharepoint Server 2019 16.0.10417.20175.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
9.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C
EPSS (30-day exploit likelihood)
70%
Higher than 99.3% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2026-55040 brief as a PDF
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Description
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Aug 18, 2026 | Aug 21, 2026 | Not reported |
| Industry KEV feed | Aug 12, 2026 | Aug 21, 2026 | Not reported |
| CIRCL KEV | Aug 12, 2026 | Aug 21, 2026 | Not reported |
| ENISA EUVD | Aug 18, 2026 | n/a | Not reported |
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.
Affected Products
9 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Sharepoint ServerMicrosoft | 2016, 2019 | 16.0.19725.20434 |
| Sharepoint Server 2016Microsoft | See advisory | 16.0.5561.1001 |
| Sharepoint Server 2019Microsoft | >= 16.0.0 | 16.0.10417.20175 |
| Microsoft SharePoint Enterprise Server 2016 | >= 16.0.0 | 16.0.5561.1001 |
| Microsoft SharePoint Server Subscription Edition | >= 16.0.0 | 16.0.19725.20434 |
Patched Releases
Microsoft SharePoint Enterprise Server 2016
16.0.5561.1001
Sharepoint Server
16.0.19725.20434
Sharepoint Server 2019
16.0.10417.20175
Microsoft SharePoint Server Subscription Edition
16.0.19725.20434
Timeline
Publicly disclosed
Jul 14, 2026
Added to Industry KEV feed
Aug 12, 2026
Added to CIRCL KEV
Aug 12, 2026
Added to CISA KEV
Aug 18, 2026
Added to ENISA EUVD
Aug 18, 2026
Last updated
Oct 8, 2026
Weakness Type
- CWE-1390 Weak Authentication
References
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
FAQ
Common Questions.
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Affected: Sharepoint Server (Microsoft) versions 2016, 2019; Sharepoint Server 2016 (Microsoft); Sharepoint Server 2019 (Microsoft) versions >= 16.0.0, among others. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Aug 12, 2026.
Yes. It was added on Aug 18, 2026 with a federal remediation due date of Aug 21, 2026.
Public exploit code is available.
Fixed versions are available, including Microsoft SharePoint Enterprise Server 2016 16.0.5561.1001, Sharepoint Server 16.0.19725.20434, Sharepoint Server 2019 16.0.10417.20175.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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