Hackers leverage new Microsoft SharePoint exploit in attacks
A critical authentication bypass vulnerability (CVE-2026-55040) in Microsoft SharePoint has been exploited using a proof-of-concept exploit published by Rapid7. The flaw allows attackers without privileges to impersonate SharePoint users or administrators, potentially disclosing files and modifying data. Microsoft patched this vulnerability in the July 2026 Patch Tuesday updates for SharePoint Enterprise Server 2016 and SharePoint Server 2019. Although exploit code is being used in attacks, there is no confirmed widespread exploitation in the wild. CISA has issued guidance to secure SharePoint servers, including limiting Internet exposure and applying Microsoft's security hardening recommendations.
AI Analysis
Technical Summary
CVE-2026-55040 is a critical authentication bypass vulnerability in Microsoft SharePoint's JWT token validation pipeline. It enables attackers without privileges to perform actions as a SharePoint site user or administrator, including data disclosure and modification, but does not affect system availability. Rapid7 published a detailed technical write-up and proof-of-concept exploit, which has already been weaponized in attacks targeting honeypots. Microsoft released a patch in the July 2026 Patch Tuesday updates addressing this flaw for SharePoint Enterprise Server 2016 and SharePoint Server 2019. CISA has warned defenders to secure SharePoint servers by avoiding unnecessary Internet exposure, blocking external access to Central Administration, restricting farm and database communications, and using application-layer security controls like reverse proxies.
Potential Impact
Exploitation of CVE-2026-55040 allows attackers to bypass authentication in Microsoft SharePoint, impersonate legitimate users or administrators, disclose sensitive files, and modify data. The vulnerability does not impact system availability. The availability of a public proof-of-concept exploit has led to its use in attacks, although no confirmed widespread exploitation has been reported. The vulnerability is considered an attractive target by Microsoft and has prompted warnings from CISA.
Mitigation Recommendations
Microsoft has released an official patch for CVE-2026-55040 as part of the July 2026 Patch Tuesday updates for SharePoint Enterprise Server 2016 and SharePoint Server 2019; applying these updates is the primary mitigation. CISA recommends avoiding direct Internet exposure of SharePoint servers unless necessary, blocking external access to SharePoint Central Administration, restricting farm and database communications to required systems, and placing servers behind Layer 7 reverse proxies or similar application-layer security controls when Internet exposure is required. Security teams should follow Microsoft's official SharePoint Server security-hardening guidance. Since the vulnerability is patched, urgent application of the update is advised.
Hackers leverage new Microsoft SharePoint exploit in attacks
Description
A critical authentication bypass vulnerability (CVE-2026-55040) in Microsoft SharePoint has been exploited using a proof-of-concept exploit published by Rapid7. The flaw allows attackers without privileges to impersonate SharePoint users or administrators, potentially disclosing files and modifying data. Microsoft patched this vulnerability in the July 2026 Patch Tuesday updates for SharePoint Enterprise Server 2016 and SharePoint Server 2019. Although exploit code is being used in attacks, there is no confirmed widespread exploitation in the wild. CISA has issued guidance to secure SharePoint servers, including limiting Internet exposure and applying Microsoft's security hardening recommendations.
Affected software
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-55040 is a critical authentication bypass vulnerability in Microsoft SharePoint's JWT token validation pipeline. It enables attackers without privileges to perform actions as a SharePoint site user or administrator, including data disclosure and modification, but does not affect system availability. Rapid7 published a detailed technical write-up and proof-of-concept exploit, which has already been weaponized in attacks targeting honeypots. Microsoft released a patch in the July 2026 Patch Tuesday updates addressing this flaw for SharePoint Enterprise Server 2016 and SharePoint Server 2019. CISA has warned defenders to secure SharePoint servers by avoiding unnecessary Internet exposure, blocking external access to Central Administration, restricting farm and database communications, and using application-layer security controls like reverse proxies.
Potential Impact
Exploitation of CVE-2026-55040 allows attackers to bypass authentication in Microsoft SharePoint, impersonate legitimate users or administrators, disclose sensitive files, and modify data. The vulnerability does not impact system availability. The availability of a public proof-of-concept exploit has led to its use in attacks, although no confirmed widespread exploitation has been reported. The vulnerability is considered an attractive target by Microsoft and has prompted warnings from CISA.
Mitigation Recommendations
Microsoft has released an official patch for CVE-2026-55040 as part of the July 2026 Patch Tuesday updates for SharePoint Enterprise Server 2016 and SharePoint Server 2019; applying these updates is the primary mitigation. CISA recommends avoiding direct Internet exposure of SharePoint servers unless necessary, blocking external access to SharePoint Central Administration, restricting farm and database communications to required systems, and placing servers behind Layer 7 reverse proxies or similar application-layer security controls when Internet exposure is required. Security teams should follow Microsoft's official SharePoint Server security-hardening guidance. Since the vulnerability is patched, urgent application of the update is advised.
Technical Details
- Classification
- {"confidence":0.64,"severitySource":"heuristic","classifier":"rss-v2"}
- Article Source
- {"url":"https://www.bleepingcomputer.com/news/microsoft/hackers-leverage-new-microsoft-sharepoint-exploit-in-attacks/","fetched":true,"fetchedAt":"2026-08-12T12:26:19.990Z","wordCount":733}
Threat ID: 6a7c666bbf8831d53986aeb4
Added to database: 08/12/2026, 12:26:19 UTC
Last enriched: 08/12/2026, 12:26:36 UTC
Last updated: 08/13/2026, 01:33:40 UTC
Views: 17
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