CriticalCVE-2026-32201

    Microsoft SharePoint Server Spoofing Vulnerability (CVE-2026-32201)

    Published Last modified In CISA KEV since Sources: CERT-EU, pwn.watch, CVE.org, Msrc Update Guide, EUVD

    What is affected, what to do

    Improper input validation in Microsoft Office SharePoint allows an unauthorized attacker to perform spoofing over a network.

    The vulnerability is being actively exploited; treat it as a priority. Update Microsoft SharePoint Enterprise Server 2016 to version 16.0.5548.1003, Microsoft SharePoint Server 2019 to version 16.0.10417.20114, Microsoft SharePoint Server Subscription Edition to version 16.0.19725.20210. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft SharePoint Enterprise Server 2016 lt 16.0.0..16.0.5548.1003
    • Microsoft SharePoint Server 2019 lt 16.0.0..16.0.10417.20114
    • Microsoft SharePoint Server Subscription Edition lt 16.0.0..16.0.19725.20210
    Fixed in
    • Microsoft SharePoint Enterprise Server 2016 16.0.5548.1003
    • Microsoft SharePoint Server 2019 16.0.10417.20114
    • Microsoft SharePoint Server Subscription Edition 16.0.19725.20210

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    6.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    6.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: CERT-EU, pwn.watch, CVE.org, Msrc Update Guide, EUVD

    43.4 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 98.7

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    226.78 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    6.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    6.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    43.4 %
    Elevated — model estimates 10-50% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    98.7
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-20

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is network-reachable without authentication or user interaction. Its nominal severity looks moderate only because the confidentiality and integrity impact is limited. Its exploitation likelihood, however, sits among the very highest of all scored CVEs, and SharePoint spoofing and validation bugs have repeatedly served as the first link in chains leading to code execution and machine-key theft. Typical targets are internet-facing on-prem farms in government, manufacturing, energy and healthcare; CISA currently does not flag ransomware use. Treat internet- or partner-exposed farms as critical with a patch deadline under 24 hours, and internal-only farms as high priority for the next emergency maintenance window.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Patch exposed farms first: Update every SharePoint server reachable from the internet or partner networks to the fixed builds: SharePoint Enterprise Server 2016 → 16.0.5548.1003, SharePoint Server 2019 → 16.0.10417.20114, Subscription Edition → 16.0.19725.20210. Look up the KB numbers in the Microsoft Security Update Guide entry for CVE-2026-32201. After installing, run the Products Configuration Wizard or PSConfig.exe -cmd upgrade -inplace b2b -wait on every farm server.
      • Verify patch level: Run (Get-SPFarm).BuildVersion on each server. A partially updated farm is still vulnerable.
      • Restrict external reach now if you cannot patch within hours: Limit publishing on the reverse proxy or application gateway to VPN or known source ranges. Alternatively, front the farm with pre-authentication (Entra ID Application Proxy, an ADFS/SAML gateway) so unauthenticated requests never reach IIS.
      • Start a compromise assessment: Preserve 30 days of IIS logs and hunt for unauthenticated hits on /_layouts/ endpoints (see Detection rules). Check …\Web Server Extensions\16\TEMPLATE\LAYOUTS\ for newly created .aspx files.
      • Rotate ASP.NET machine keys if anything looks suspicious: Spoofing bugs can be the entry point for key-theft chains. After patching, run Set-SPMachineKey or Update-SPMachineKey per web application, then iisreset on all servers.
      • Check NIS2 reporting: If exploitation is confirmed, prepare the 24-hour early warning to your national CSIRT (BSI in Germany).

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place SharePoint front-ends in a DMZ or application zone. Default-deny outbound internet traffic from farm servers, allowing only Microsoft Update endpoints or your WSUS proxy, to hamper payload staging and exfiltration.
      • WAF/reverse proxy: Block or challenge unauthenticated POSTs to /_layouts/15/*.aspx. Log and rate-limit requests whose Referer points at sign-out or sign-in pages (e.g. /_layouts/SignOut.aspx) while hitting administrative pages. Enable vendor signatures for CVE-2026-32201 (F5, Azure WAF, FortiWeb) as soon as they ship.
      • Endpoint hardening: Enable SharePoint AMSI integration (Central Administration → Security → Antimalware Scan Interface, Full Mode where supported) with up-to-date Defender or equivalent on all farm servers. Add EDR policies blocking shells spawned by w3wp.exe.
      • IAM/least privilege: Disable anonymous access on web applications and site collections unless there is a hard business need. Ensure the farm account and app-pool identities hold no Domain Admin rights, and rotate service-account passwords after patching.
      • Configuration: Turn off unused service applications and legacy auth providers (NTLM-only zones exposed externally). Run the extranet zone with claims-based sign-in via an IdP enforcing MFA.

    3. Runbook step 3

      Detection rules

      • IIS access logs (W3C): Look for unauthenticated calls to administrative layouts pages. Example SPL: index=iis cs_uri_stem="*/_layouts/15/*" cs_method=POST cs_username="-" sc_status=200 | stats count by c_ip, cs_uri_stem, cs_Referer. An odd or foreign cs(Referer) on sensitive endpoints is a strong signal.
      • EDR process ancestry (Sysmon EID 1 / MDE): DeviceProcessEvents | where InitiatingProcessFileName =~ "w3wp.exe" and FileName in~ ("cmd.exe","powershell.exe","pwsh.exe","csc.exe","certutil.exe"). On SharePoint hosts, this is almost always malicious.
      • File creation (Sysmon EID 11 / MDE): DeviceFileEvents | where FolderPath has @"\TEMPLATE\LAYOUTS\" and FileName endswith ".aspx" and ActionType == "FileCreated". Escalate new webshells (spinstall*.aspx, randomly named pages) immediately.
      • Windows/AMSI telemetry: Defender Event ID 1116/1117 with w3wp.exe as the source process, plus AMSI detections in the SharePoint context. Use a Sigma process_creation rule with ParentImage|endswith: '\w3wp.exe' as the baseline.
      • Network (Zeek/Suricata): Watch for outbound connections from farm servers to unknown external IPs, especially right after POSTs to /_layouts/. Query Zeek conn.log filtered on the farm subnet with id.resp_p outside approved update ports.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    Improper input validation in Microsoft Office SharePoint allows an unauthorized attacker to perform spoofing over a network.

    Source: certeu_advisory, pwn.watch, cvelistv5, Microsoft Security Update Guide, ENISA EUVD, NVD (NIST), CISA KEV Catalog, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    MicrosoftMicrosoft SharePoint Enterprise Server 2016
    • 16.0.0 – < 16.0.5548.1003
    • 16.0.5548.1003
    MicrosoftMicrosoft SharePoint Server 2019
    • 16.0.0 – < 16.0.10417.20114
    • 16.0.10417.20114
    MicrosoftMicrosoft SharePoint Server Subscription Edition
    • 16.0.0 – < 16.0.19725.20210
    • 16.0.19725.20210
    microsoftsharepoint_server
    • 2019
    • 2016
    • < 16.0.19725.20210
    • —
    • —
    • 16.0.19725.20210

    Vendors and products

    Weakness classes (CWE)

    • CWE-20Improper Input Validation

      Class

      The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

      Entry at MITRE CWE-20

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • Microsoft Security Update GuideMicrosoft SharePoint Server Spoofing Vulnerabilityeuvd, Vendor advisory, Patch, Vendor advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-32201government-resource, Third-party advisory, US government resource
    • pwn.watchpwn.watch: Microsoft SharePoint Server: Microsoft SharePoint Server Improper Input Validation Vulnerabilitypwn-watch
    • Microsoft Security Update GuideMicrosoft SharePoint Server — CVE-2026-32201pwn-watch
    • NVD (NIST)NVD: CVE-2026-32201pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    One NVD translation into another language is hidden.

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