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Known Exploited Vulnerability
9.1
CRITICAL CVSS 3.1
CVE-2026-55040
Microsoft SharePoint Weak Authentication Vulnerability - [Actively Exploited]
Overview
Description

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

Details
INFO

Published Date :

July 14, 2026, 6:18 p.m.

Last Modified :

Aug. 19, 2026, 4:17 a.m.

Remotely Exploit :

No

Source :

[email protected]
CISA Notification
CISA KEV (Known Exploited Vulnerabilities)

For the benefit of the cybersecurity community and network defenders—and to help every organization better manage vulnerabilities and keep pace with threat activity—CISA maintains the authoritative source of vulnerabilities that have been exploited in the wild.

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.

Known Ransomware Campaign Use:

Unknown

Notes :

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

Impact
Affected Products

The following products are affected by CVE-2026-55040 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Microsoft sharepoint_server
2 Microsoft sharepoint_enterprise_server_2016
3 Microsoft sharepoint_server_2016
4 Microsoft sharepoint_server_2019
: Total Affected Vendor : 1 | Products : 4
Scoring
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 134c704f-9b21-4f2e-91b3-4a467353bcc0
CVSS 3.1 CRITICAL f38d906d-7342-40ea-92c1-6c4a2c6478c8
CVSS 3.1 CRITICAL [email protected]
References
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2026-55040.

URL Resource
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 Patch Vendor Advisory
https://github.com/sfewer-r7/CVE-2026-55040 Exploit
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040 Exploit Third Party Advisory
https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/ US Government Resource
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-55040 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-55040 weaknesses.

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-55040 vulnerability anywhere in the article.

  • The Hacker News
ThreatsDay: 296K IoT Botnet, 100+ Water Systems Targeted, SharePoint RCE Chain + 27 New Stories

A fake login page. A fake security scan. A fake productivity app. Apparently, pretending to be useful is still one of the easier ways into a machine.The rest of the week gets stranger: botnets borrowi ... Read more

Published Date: Aug 27, 2026 (5 days, 2 hours ago)
  • security.nl
Belangrijk beveiligingslek in Microsoft SharePoint misbruikt bij aanvallen

donderdag 27 augustus 2026, 10:27 door Redactie, 2 reactiesLaatst bijgewerkt: Vandaag, 10:31 Een belangrijke kwetsbaarheid in Microsoft SharePoint die remote code execution (RCE) mogelijk maakt, en wa ... Read more

Published Date: Aug 27, 2026 (5 days, 9 hours ago)
  • TheCyberThrone
CISA Adds Five Actively Exploited Vulnerabilities to KEV in Just Two Days

A Five-Vulnerability Warning: From AI Infrastructure to Virtualization and Enterprise CollaborationThe U.S. Cybersecurity and Infrastructure  Security Agency (CISA) has added five vulnerabilities to i ... Read more

Published Date: Aug 20, 2026 (1 week, 5 days ago)
  • The Hacker News
Critical macOS, SharePoint, vCenter, and Microsoft IKE Flaws Under Active Exploitation

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) on Tuesday added four critical vulnerabilities to its Known Exploited Vulnerabilities (KEV) catalog, stating they are being exploited i ... Read more

Published Date: Aug 19, 2026 (1 week, 6 days ago)
  • security.nl
Microsoft SharePoint-lek misbruikt na verschijnen proof-of-concept exploit

Een kritieke kwetsbaarheid in Microsoft SharePoint is kort na publicatie van de proof-of-concept exploitcode door cybersecuritybedrijf Rapid7 misbruikt bij aanvallen. Dat beweert it-beveiliger Defused ... Read more

Published Date: Aug 13, 2026 (2 weeks, 5 days ago)
  • The Hacker News
Attackers Exploit SharePoint Authentication Bypass After Public PoC Release

Threat actors have begun to exploit a newly disclosed Microsoft SharePoint vulnerability following the release of a proof-of-concept (PoC) code. The vulnerability in question is CVE-2026-55040 (CVSS s ... Read more

Published Date: Aug 13, 2026 (2 weeks, 5 days ago)
  • The Hacker News
Microsoft Patches 398 Flaws Including a Windows Driver Zero-Day Under Active Attack

Microsoft released its monthly security updates on Tuesday, and one of the flaws it closed is already being used in attacks. The bug sits in a core Windows kernel driver that handles network socket op ... Read more

Published Date: Aug 11, 2026 (2 weeks, 6 days ago)
  • The Hacker News
Researchers Disclose AI-Assisted SharePoint Exploit Chain Reaching Unauthenticated RCE

Security researchers found a way to enter Microsoft SharePoint servers as any user, including an administrator, with no valid account. A significant part of the work that found it was done through an ... Read more

Published Date: Aug 11, 2026 (3 weeks ago)
  • Kaspersky
Key vulnerabilities of Microsoft’s July 2026 Patch Tuesday

Although experts had already warned of an impending “tsunami of vulnerabilities” back in April, immediately following the announcement of the Mythos AI model, concrete evidence began to emerge over th ... Read more

Published Date: Jul 15, 2026 (1 month, 2 weeks ago)
  • The Hacker News
Researcher Drops New Windows Zero-Day PoC Hours After Microsoft Patch Tuesday

Security researcher Chaotic Eclipse (aka Nightmare-Eclipse) has released a new proof-of-concept (PoC) exploit called LegacyHive. It has been described as a Windows User Profile Service arbitrary hive ... Read more

Published Date: Jul 15, 2026 (1 month, 2 weeks ago)
  • security.nl
Microsoft SharePoint-servers aangevallen, VS roept op tot extra beveiliging

Aanvallers maken actief misbruik van verschillende kwetsbaarheden voor het aanvallen van Microsoft SharePoint-servers, zo waarschuwt het Amerikaanse cyberagentschap CISA. Dat roept organisaties op om ... Read more

Published Date: Jul 15, 2026 (1 month, 2 weeks ago)
  • CrowdStrike.com
July 2026 Patch Tuesday: Microsoft Patches 622 Vulnerabilities Including Two Exploited Zero-Days

Microsoft has addressed 622 vulnerabilities in its July 2026 security update release. Based on CrowdStrike’s analysis, this represents roughly triple the number of vulnerabilities in June, and almost ... Read more

Published Date: Jul 15, 2026 (1 month, 2 weeks ago)
  • The Hacker News
Microsoft Patches Record 622 Flaws, Including Two Zero-Days Under Active Attack

Microsoft shipped its largest Patch Tuesday on record today, and two of the fixes close holes that attackers are already exploiting. The release covers 622 of Microsoft's own CVEs by its Security Upda ... Read more

Published Date: Jul 14, 2026 (1 month, 2 weeks ago)

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2026-55040 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Aug. 19, 2026

    Action Type Old Value New Value
    Changed SSVC {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'active'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-08-18T17:44:14.794727Z'} {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'active'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-13T00:00:00+00:00'}
  • Modified Analysis by [email protected]

    Aug. 18, 2026

    Action Type Old Value New Value
    Added Reference Type CISA-ADP: https://github.com/sfewer-r7/CVE-2026-55040 Types: Exploit
    Added Reference Type CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040 Types: Exploit, Third Party Advisory
    Added Reference Type CISA-ADP: https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/ Types: US Government Resource
  • CVE CISA KEV Update by 9119a7d8-5eab-497f-8521-727c672e3725

    Aug. 18, 2026

    Action Type Old Value New Value
    Added Date Added 2026-08-18
    Added Due Date 2026-08-18
    Added Required Action 2026-08-18
    Added Vulnerability Name 2026-08-18
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Aug. 18, 2026

    Action Type Old Value New Value
    Added Reference https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040
    Changed SSVC {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-08-13T03:55:25.706009Z'} {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'active'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-08-18T17:44:14.794727Z'}
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Aug. 13, 2026

    Action Type Old Value New Value
    Added Reference https://github.com/sfewer-r7/CVE-2026-55040
    Added Reference https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/
    Changed SSVC {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-13T00:00:00+00:00'} {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-08-13T03:55:25.706009Z'}
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Aug. 13, 2026

    Action Type Old Value New Value
    Changed SSVC {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-13T00:00:00+00:00'} {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-13T00:00:00+00:00'}
  • Initial Analysis by [email protected]

    Jul. 15, 2026

    Action Type Old Value New Value
    Added CPE Configuration OR *cpe:2.3:a:microsoft:sharepoint_server:2019:*:*:*:*:*:*:* *cpe:2.3:a:microsoft:sharepoint_server:2016:*:*:*:enterprise:*:*:* *cpe:2.3:a:microsoft:sharepoint_server:*:*:*:*:subscription:*:*:* versions up to (excluding) 16.0.19725.20434
    Added Reference Type Microsoft Corporation: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 Types: Patch, Vendor Advisory
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Jul. 15, 2026

    Action Type Old Value New Value
    Changed SSVC {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-14T18:57:00.469823Z'} {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-13T00:00:00+00:00'}
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Jul. 14, 2026

    Action Type Old Value New Value
    Added SSVC {'id': 'CVE-2026-55040', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-14T18:57:00.469823Z'}
  • New CVE Received by [email protected]

    Jul. 14, 2026

    Action Type Old Value New Value
    Added Affected [{'vendor': 'Microsoft', 'product': 'Microsoft SharePoint Enterprise Server 2016', 'versions': [{'status': 'affected', 'version': '16.0.0', 'lessThan': '16.0.5561.1001', 'versionType': 'custom'}], 'platforms': ['x64-based Systems']}, {'vendor': 'Microsoft', 'product': 'Microsoft SharePoint Server 2019', 'versions': [{'status': 'affected', 'version': '16.0.0', 'lessThan': '16.0.10417.20175', 'versionType': 'custom'}], 'platforms': ['x64-based Systems']}, {'vendor': 'Microsoft', 'product': 'Microsoft SharePoint Server Subscription Edition', 'versions': [{'status': 'affected', 'version': '16.0.0', 'lessThan': '16.0.19725.20434', 'versionType': 'custom'}], 'platforms': ['x64-based Systems']}]
    Added Description Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
    Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
    Added CWE CWE-1390
    Added Reference https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
CVSS
Vulnerability Scoring Details
Base CVSS Score: 9.1
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact