CVE-2026-55040 (GCVE-0-2026-55040)
Vulnerability from cvelistv5 – Published: 2026-07-14 17:09 – Updated: 2026-09-25 18:24Title
Microsoft SharePoint Server Security Feature Bypass Vulnerability
Summary
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Severity
9.1 (Critical)
SSVC
Exploitation: active
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-13 00:00 UTC
CWE
- CWE-1390 - Weak Authentication
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://msrc.microsoft.com/update-guide/vulnerabi… | vendor-advisorypatch |
| https://www.rapid7.com/blog/post/ra-microsoft-sha… | technical-description |
| https://github.com/sfewer-r7/CVE-2026-55040 | exploit |
| https://www.cisa.gov/known-exploited-vulnerabilit… | government-resource |
Impacted products
3 products
| Vendor | Product | Version | |
|---|---|---|---|
| Microsoft | Microsoft SharePoint Enterprise Server 2016 |
Affected:
16.0.0 , < 16.0.5561.1001
(custom)
|
|
| Microsoft | Microsoft SharePoint Server 2019 |
Affected:
16.0.0 , < 16.0.10417.20175
(custom)
|
|
| Microsoft | Microsoft SharePoint Server Subscription Edition |
Affected:
16.0.0 , < 16.0.19725.20434
(custom)
|
Date Public
2026-07-14 14:00
CISA
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 7176ca67-d798-46de-8f14-0f08ebe8601c
Exploited: Yes
Timestamps
First Seen: 2026-08-18
Asserted: 2026-08-18
Scope
Notes: Microsoft SharePoint Weak Authentication Vulnerability | Affected: Microsoft / SharePoint | Description: Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network. | 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 date: 2026-08-21 | Known ransomware campaign use (KEV): Unknown | Notes (KEV): https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2026-55040
Evidence
Type: Vendor Report
Signal: Successful Exploitation
Confidence: 80%
Source: cisa-kev
Details
| Cwes | CWE-1390 |
|---|---|
| Feed | CISA Known Exploited Vulnerabilities Catalog |
| Product | SharePoint |
| Due Date | 2026-08-21 |
| Date Added | 2026-08-18 |
| Vendorproject | Microsoft |
| Vulnerabilityname | Microsoft SharePoint Weak Authentication Vulnerability |
| Knownransomwarecampaignuse | Unknown |
References
Created: 2026-10-02 08:09 CEST
| Updated: 2026-10-02 08:09 CEST
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 1c4d902f-03d7-40f9-a428-0fb8587dbd7c
Exploited: Yes
Timestamps
First Seen: 2026-08-12
Asserted: 2026-08-12
Scope
Notes: Microsoft SharePoint Server Security Feature Bypass Vulnerability | Affected: Microsoft / Microsoft SharePoint Enterprise Server 2016, Microsoft SharePoint Server 2019, Microsoft SharePoint Server Subscription Edition | CVSS: 9.1 (CRITICAL) | EPSS: 0.17535 | Used in malware: unknown | Listed 7 days ahead of CISA KEV | Not yet in CISA KEV: False
Evidence
Type: Public Report
Signal: Successful Exploitation
Confidence: 70%
Source: previdian
Details
| Feed | Previdian (previdian.com) |
|---|---|
| Title | Microsoft SharePoint Server Security Feature Bypass Vulnerability |
| Cve Id | CVE-2026-55040 |
| Vendor | Microsoft |
| Ghsa Id | GHSA-GRXW-7CVC-96RV |
| Product | Microsoft SharePoint Enterprise Server 2016, Microsoft SharePoint Server 2019, Microsoft SharePoint Server Subscription Edition |
| Added Date | 2026-08-12T19:37:46.763Z |
| Cvss Score | 9.1 |
| Epss Score | 0.17535 |
| Previous Ids | |
| Cvss Severity | CRITICAL |
| Virtual Patch | False |
| Cvss Estimated | False |
| Epss Percentile | 0.97051 |
| Used In Malware | unknown |
| Vulnerability Id | CVE-2026-55040 |
| Ahead Of Cisa Kev |
|
| Not Yet In Cisa Kev | False |
References
Created: 2026-10-02 09:09 CEST
| Updated: 2026-10-02 09:09 CEST
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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