{"cve":{"cve_id":"CVE-2026-55040","is_kev":true,"kev_date_added":"2026-08-18","kev_vendor_project":"Microsoft","kev_product":"SharePoint","kev_vulnerability_name":"Microsoft SharePoint Weak Authentication Vulnerability","kev_short_description":"Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.","kev_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.","kev_due_date":"2026-08-21","kev_known_ransomware":false,"kev_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","kev_cwes":["CWE-1390"],"epss_score":0.05578,"epss_percentile":0.92293,"epss_as_of":"2026-08-26","description":"Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.","published_at":"2026-07-14T17:09:00.641000Z","last_modified_at":"2026-08-19T04:17:23.540000Z","cvss_v3_score":9.1,"cvss_v3_vector":"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","cvss_v3_severity":"CRITICAL","cvss_v4_score":null,"cvss_v4_vector":null,"cvss_v4_severity":null,"ssvc_decision":null,"ssvc_exploitation":"active","ssvc_automatable":true,"ssvc_technical_impact":"total","cwes":["CWE-1390"],"nvd_references":["https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040"],"vuln_status":"Analyzed","trending_score":null,"is_trending":false,"has_trended":false,"trended_number_one":false,"trending_peak_score":null,"trending_peak_rank":null,"started_trending_at":null,"trended_number_one_at":null,"summary_generated":null,"summary_generated_at":null,"summary_model":null,"created_at":"2026-07-14T18:33:20.779180Z","updated_at":"2026-08-19T16:41:57.515079Z"},"effective_severity":"CRITICAL","badges":["kev","poc","news"],"impact_analysis":[],"cvss_v3_decoded":{"version":"3.1","metrics":[{"metric":"AV","name":"Attack Vector","value":"N","value_label":"Network"},{"metric":"AC","name":"Attack Complexity","value":"L","value_label":"Low"},{"metric":"PR","name":"Privileges Required","value":"N","value_label":"None"},{"metric":"UI","name":"User Interaction","value":"N","value_label":"None"},{"metric":"S","name":"Scope","value":"U","value_label":"Unchanged"},{"metric":"C","name":"Confidentiality","value":"H","value_label":"High"},{"metric":"I","name":"Integrity","value":"H","value_label":"High"},{"metric":"A","name":"Availability","value":"N","value_label":"None"},{"metric":"E","name":"E","value":"U","value_label":"Unchanged"},{"metric":"RL","name":"RL","value":"O","value_label":"O"},{"metric":"RC","name":"RC","value":"C","value_label":"Changed"}]},"cvss_v4_decoded":{"version":null,"metrics":[]},"affected":[{"vendor_slug":"microsoft","vendor_name":"microsoft","product_slug":"microsoft-sharepoint-enterprise-server-2016","product_name":"Microsoft SharePoint Enterprise Server 2016","version_start":"16.0.0","version_start_inclusive":true,"version_end":"16.0.5561.1001","version_end_inclusive":false,"cpe23_uri":"cve5:microsoft:microsoft-sharepoint-enterprise-server-2016:16.0.0:16.0.5561.1001"},{"vendor_slug":"microsoft","vendor_name":"microsoft","product_slug":"microsoft-sharepoint-server-2019","product_name":"Microsoft SharePoint Server 2019","version_start":"16.0.0","version_start_inclusive":true,"version_end":"16.0.10417.20175","version_end_inclusive":false,"cpe23_uri":"cve5:microsoft:microsoft-sharepoint-server-2019:16.0.0:16.0.10417.20175"},{"vendor_slug":"microsoft","vendor_name":"microsoft","product_slug":"microsoft-sharepoint-server-subscription-edition","product_name":"Microsoft SharePoint Server Subscription Edition","version_start":"16.0.0","version_start_inclusive":true,"version_end":"16.0.19725.20434","version_end_inclusive":false,"cpe23_uri":"cve5:microsoft:microsoft-sharepoint-server-subscription-edition:16.0.0:16.0.19725.20434"},{"vendor_slug":"microsoft","vendor_name":"microsoft","product_slug":"sharepoint-server","product_name":"sharepoint_server","version_start":null,"version_start_inclusive":null,"version_end":"16.0.19725.20434","version_end_inclusive":false,"cpe23_uri":"cpe:2.3:a:microsoft:sharepoint_server:*:*:*:*:subscription:*:*:*"},{"vendor_slug":"microsoft","vendor_name":"microsoft","product_slug":"sharepoint-server","product_name":"sharepoint_server","version_start":"2016","version_start_inclusive":true,"version_end":"2016","version_end_inclusive":true,"cpe23_uri":"cpe:2.3:a:microsoft:sharepoint_server:2016:*:*:*:enterprise:*:*:*"},{"vendor_slug":"microsoft","vendor_name":"microsoft","product_slug":"sharepoint-server","product_name":"sharepoint_server","version_start":"2019","version_start_inclusive":true,"version_end":"2019","version_end_inclusive":true,"cpe23_uri":"cpe:2.3:a:microsoft:sharepoint_server:2019:*:*:*:*:*:*:*"}],"exploit_refs":[{"source":"nuclei","kind":"nuclei","url":"https://github.com/projectdiscovery/nuclei-templates/blob/main/javascript/cves/2026/CVE-2026-55040.yaml","title":"Microsoft SharePoint Server - JWT Authentication Bypass","author":"sfewer-r7,DhiyaneshDk","disclosed_at":null}],"news":[{"id":1174,"source":"The Hacker News","url":"https://thehackernews.com/2026/08/attackers-exploit-sharepoint.html","title":"Attackers Exploit SharePoint Authentication Bypass After Public PoC Release","summary":"Threat actors have begun to exploit a newly disclosed Microsoft SharePoint vulnerability following the release of a proof-of-concept (PoC) code.\n\nThe vulnerability in question is CVE-2026-55040 (CVSS score: 9.1), which refers to a critical security feature bypass that stems from weak authentication. It was patched by Microsoft as part of its July 2026 Patch Tuesday updates.\n\n\"The authentication","thumbnail_url":"https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_e1WsuZlqC_AfMpdI4wXB0wzIA6nGpPb5ktYmwO5jRhFqH2t56eGghhYAV7he6u0qTqiPacKD-Wf3c1vXxUmBV159KAObOJUTEDGdDafl9B0makdRgyKTUwWHZ5qxLpGbWRg33JJl_0KaY0K0fiWLaV2xghWX4KqUSeaoNgD9Z5ql1Q5VesZQyH-1eO7W/s1600/poc.jpg","author":"info@thehackernews.com (The Hacker News)","published_at":"2026-08-13T06:09:48Z","fetched_at":"2026-08-13T06:48:53.296677Z","trending_score":0.008691025438575336,"cve_ids":["CVE-2026-55040"]},{"id":1130,"source":"The Hacker News","url":"https://thehackernews.com/2026/08/researchers-disclose-ai-assisted.html","title":"Researchers Disclose AI-Assisted SharePoint Exploit Chain Reaching Unauthenticated RCE","summary":"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 AI agent.\n\nThe flaw, tracked as CVE-2026-55040 (CVSS 9.1), affects SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Server 2016. Microsoft's","thumbnail_url":"https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbDSDTAbeeAZ8pykGFRAGcCDs_3LZBuD8tYUJfh0jG35r_o84zM_bNo7q3TWcoEMPmZqvhzucujEF72b2c2HnzfDjowsj4Iw4psQEwcgADR_rVMCXVw18arcpSB0WLblkZeypa-bgJPsD0qwrqBUk2umKezFZTtuDpbi_kQlsGUSiveb2suBMRyc3oZhQ/s1600/admin.jpg","author":"info@thehackernews.com (The Hacker News)","published_at":"2026-08-11T16:47:44Z","fetched_at":"2026-08-11T17:59:50.365765Z","trending_score":0.005066646016079121,"cve_ids":["CVE-2026-55040"]}],"references":[{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040","source_type":"VENDOR_ADVISORY","tags":["advisory"]}],"timeline":[{"type":"published","at":"2026-07-14T17:09:00.641000Z","label":"CVE published","source":null},{"type":"ssvc_changed","at":"2026-07-14T20:34:20.783664Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"ssvc_changed","at":"2026-07-14T20:34:20.783664Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"ssvc_changed","at":"2026-07-14T20:34:20.783664Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"first_article","at":"2026-08-11T16:47:44Z","label":"First news coverage","source":"The Hacker News"},{"type":"ssvc_changed","at":"2026-08-13T14:21:52.867270Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"cisa_reported","at":"2026-08-18T00:00:00Z","label":"Added to CISA KEV catalog","source":"kev"},{"type":"ssvc_changed","at":"2026-08-18T20:43:27.518524Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"poc_available","at":"2026-08-26T17:38:11.388928Z","label":"Public PoC available","source":"nuclei"}]}