{"id":"CVE-2026-45659","kind":"vulnerability","aliases":["CVE-2026-45659"],"related":[],"title":"microsoft sharepoint server: Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over…","description":"Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.\n\nCISA 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.","summary":"Microsoft SharePoint Server has a deserialization of untrusted data flaw that lets an authorized attacker run code over the network. CISA lists it as actively exploited, with ransomware use noted in the tags.","severity":"high","cvss":8.8,"epss":null,"exploited":true,"exploited_at":"2026-07-01T00:00:00+00:00","products":[{"name":"microsoft sharepoint server","fixed":["16.0.19725.20280"],"affected":"< 16.0.19725.20280","ecosystem":"vendor"},{"name":"microsoft sharepoint server","fixed":[],"affected":"= 2016","ecosystem":"vendor"},{"name":"microsoft sharepoint server","fixed":[],"affected":"= 2019","ecosystem":"vendor"},{"name":"Microsoft SharePoint Server","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","ransomware","self-hosted","sharepoint-server","vendor","windows"],"not_affected_if":["managed-hosting","sharepoint-online"],"how_to_check":"Identify SharePoint Server instances in your environment and confirm their build against Microsoft's security update guide for CVE-2026-45659; the sources do not give a specific build number or command.","fix":"Apply the Microsoft SharePoint Server security update for CVE-2026-45659, or the vendor mitigation if no patch is available; the sources do not name the fixed version. If mitigations are unavailable, discontinue use of the product per CISA guidance.","status":"open","published_at":"2026-05-22T23:16:56+00:00","first_seen_at":"2026-10-23T19:11:51+00:00","triaged_at":"2026-10-23T20:33:46+00:00","updated_at":"2026-10-24T00:09:50+00:00","category":"vendor","confidence":0.6,"triage":{"at":"2026-10-23T20:33:46Z","model":"claude-haiku-5-5","output":{"fix":"Apply the Microsoft SharePoint Server security update for CVE-2026-45659, or the vendor mitigation if no patch is available; the sources do not name the fixed version. If mitigations are unavailable, discontinue use of the product per CISA guidance.","summary":"Microsoft SharePoint Server has a deserialization of untrusted data flaw that lets an authorized attacker run code over the network. CISA lists it as actively exploited, with ransomware use noted in the tags.","category":"vendor","who_cares":["sharepoint-server","self-hosted","windows"],"confidence":0.6,"analyst_note":"Find the fixed build and vendor mitigation in Microsoft's security update guide for CVE-2026-45659, and confirm whether SharePoint Online is affected.","how_to_check":"Identify SharePoint Server instances in your environment and confirm their build against Microsoft's security update guide for CVE-2026-45659; the sources do not give a specific build number or command.","needs_analyst":true,"not_affected_if":["sharepoint-online","managed-hosting"],"severity_if_unknown":"high"},"cost_usd":0.000412,"input_tokens":2209,"output_tokens":383,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-04':118C,144C,175C '-2026':20A,23A '-45659':21A,24A '26':117C,143C,174C 'accord':107C 'action':103C 'activ':71B 'adher':171C 'allow':12A,91C 'appli':104C 'applic':141C 'asset':165C 'attack':15A,61B,94C 'author':14A,60B,93C 'base':122C 'bod':116C,142C,173C 'cisa':67B,101C,114C,131C 'cloud':147C 'code':18A,63B,97C 'complianc':112C 'contain':83C 'cve':19A,22A 'data':7A,55B,88C 'deseri':4A,52B,85C 'discontinu':150C 'ensur':111C,170C 'evalu':163C 'execut':17A,96C 'exploit':37B,72B 'exposur':168C 'flaw':56B 'follow':140C 'forens':133C 'guidanc':129C,145C 'guidelin':177C 'host':41B 'instruct':110C 'internet':167C 'let':58B 'list':68B 'microsoft':1A,9A,25A,28A,31A,34A,47B,80C 'mitig':105C,156C 'network':66B,100C 'note':76B,128C,139C 'offic':10A 'patch':176C 'priorit':119C 'product':154C 'ransomwar':38B,74B 'requir':102C,135C 'respons':161C 'risk':124C 'run':62B 'secur':120C 'see':125C,136C 'self':40B 'self-host':39B 'server':3A,27A,30A,33A,36A,44B,49B,82C 'servic':148C 'sharepoint':2A,11A,26A,29A,32A,35A,43B,48B,81C 'sharepoint-serv':42B 'stakehold':159C 'tag':79B 'triag':134C 'unavail':158C 'untrust':6A,54B,87C 'updat':121C 'url':126C,137C 'use':75B,151C 'vendor':45B,109C 'vulner':89C 'window':46B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2026-05-22T23:16:56+00:00","kev":{"dateAdded":"2026-07-01","dueDate":"2026-07-04","requiredAction":"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.","knownRansomwareCampaignUse":"Known"},"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvss_by":"secure@microsoft.com","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2026-45659","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-45659","severity":null,"published_at":"2026-07-01T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:51+00:00","fetched_at":"2026-10-25T10:39:04+00:00","note":null},{"source":"nvd","external_id":"CVE-2026-45659","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-45659","severity":null,"published_at":"2026-05-22T23:16:56+00:00","modified_at":"2026-07-23T11:10:00+00:00","first_seen_at":"2026-10-23T23:44:51+00:00","fetched_at":"2026-10-23T23:44:51+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}