CriticalCVE-2025-49706

    Microsoft SharePoint Server Spoofing Vulnerability (CVE-2025-49706)

    Published In CISA KEV since Sources: SingCERT, NCSC NZ, pwn.watch, CERT-EU, Msrc Update Guide, CVE.org

    What is affected, what to do

    Improper authentication 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. CISA lists it as used in ransomware campaigns. Update Microsoft SharePoint Enterprise Server 2016 to version 16.0.5508.1000, Microsoft SharePoint Server 2019 to version 16.0.10417.20027, Microsoft SharePoint Server Subscription Edition to version 16.0.18526.20424. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft SharePoint Enterprise Server 2016 lt 16.0.0..16.0.5508.1000
    • Microsoft SharePoint Server 2019 lt 16.0.0..16.0.10417.20027
    • Microsoft SharePoint Server Subscription Edition lt 16.0.0..16.0.18526.20424
    Fixed in
    • Microsoft SharePoint Enterprise Server 2016 16.0.5508.1000
    • Microsoft SharePoint Server 2019 16.0.10417.20027
    • Microsoft SharePoint Server Subscription Edition 16.0.18526.20424

    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: SingCERT, NCSC NZ, pwn.watch, CERT-EU, Msrc Update Guide, CVE.org

    99.06 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.93

    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
    247.20 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), NCSC NZ, CSA/SingCERT 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
    99.06 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    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
    99.93
    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-287

    Response and mitigation

    Why act now?

    Prioritisation rationale

    CVE-2025-49706 is the authentication-bypass half of the "ToolShell" chain. Combined with CVE-2025-49704, it gives unauthenticated remote code execution on internet-facing SharePoint, followed by theft of the farm's machine keys for persistent access. The standalone severity rating looks moderate but understates the real risk considerably: the flaw is network-reachable without authentication, functional exploit code is public, and its exploitation likelihood ranks among the very highest of all CVEs. CISA also flags the campaign for known ransomware use. Typical victims are public sector bodies, critical infrastructure operators and mid-market firms running self-hosted collaboration platforms. Treat any externally reachable on-premises farm as a drop-everything item, including key rotation and a compromise assessment. Internal-only farms belong at the top of the regular emergency patch window.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Identify exposed SharePoint servers: Enumerate all on-premises farms (SharePoint Server 2016, 2019, Subscription Edition) and confirm which are reachable from the internet on TCP 80/443, whether directly, via a reverse proxy or via WAF publishing. SharePoint Online (Microsoft 365) is not affected.
      • Patch with the CVE-2025-53771/CVE-2025-53770 updates, not just the CVE-2025-49706 fix: The newer updates close the patch bypass and provide more robust protection than the original fix. Patches are available from the vendor; look up the build and KB numbers per product version in the Microsoft advisory. Run PSConfig or the Products Configuration Wizard after installing.
      • Pull the server off the internet if you cannot patch: If immediate patching is impossible or the version is out of support, cut internet exposure at the firewall or unpublish the site at the reverse proxy.
      • Rotate ASP.NET machine keys: The exploit chain is used to steal ValidationKey and DecryptionKey. After patching, run Update-SPMachineKey or trigger the "Machine Key Rotation Job" in Central Administration. Then run iisreset.exe on every farm server. Without this step, attackers can keep forging signed __VIEWSTATE payloads even on a patched farm.
      • Start a compromise assessment: Hunt for new or unknown .aspx files in C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\TEMPLATE\LAYOUTS\, such as spinstall*.aspx. Review IIS logs back to mid-July 2025 (see Detection rules). Any hit means the farm should be treated as compromised: open an incident and assess NIS2 reporting obligations.

    2. Runbook step 2

      Mitigation layers

      • Endpoint hardening: Enable SharePoint AMSI integration in Full Mode. Run Microsoft Defender Antivirus, or an AMSI-capable EDR, on all SharePoint servers. AMSI blocks known payloads from the CVE-2025-49704 chain before deserialisation occurs.
      • WAF/IPS: Block requests to /_layouts/15/ToolPane.aspx (and /_layouts/16/) whose Referer header contains /_layouts/SignOut.aspx. This is the signature pattern of the authentication bypass. Also alert on DisplayMode=Edit in the query string and on unusually large POST bodies sent to ToolPane endpoints.
      • Network segmentation: Publish SharePoint only behind a pre-authenticating proxy, such as Entra Application Proxy or a VPN gateway, so anonymous requests never reach IIS. Restrict outbound traffic from SharePoint servers to required destinations (updates, CRL) to block second-stage downloads and exfiltration.
      • IAM/least privilege: Review the rights of the application pool identities (w3wp.exe) and remove local admin or domain privileges they do not need. If a compromise is confirmed, plan rotation of farm and service account credentials, including AD and SQL accounts.
      • Lifecycle: SharePoint 2010 and 2013 receive no fixes. Isolate or migrate these systems; compensating controls alone are insufficient.

    3. Runbook step 3

      Detection rules

      • IIS access logs (W3C format with the Referer field enabled): Look for POST requests to ToolPane.aspx with a SignOut.aspx referer. SPL: index=iis cs_method=POST cs_uri_stem="*/_layouts/1*/ToolPane.aspx" cs_Referer="*/_layouts/SignOut.aspx*"
      • Sysmon EID 11 / EDR file events: Detect .aspx files written to TEMPLATE\LAYOUTS by w3wp.exe or one of its children. KQL: DeviceFileEvents | where FolderPath has @"\TEMPLATE\LAYOUTS\" and FileName endswith ".aspx" and InitiatingProcessFileName in~ ("w3wp.exe","cmd.exe","powershell.exe")
      • Process ancestry (Sysmon EID 1 / Security EID 4688): Alert on w3wp.exe → cmd.exe → powershell.exe, especially with -EncodedCommand or -ec. Sigma shape: ParentImage|endswith: '\w3wp.exe' combined with Image|endswith: ['\cmd.exe','\powershell.exe'].
      • Machine key theft follow-up: Watch for GET requests to newly created .aspx files under /_layouts/15/, which can indicate key dumping. Also flag POST requests carrying oversized __VIEWSTATE values to arbitrary pages that are followed by process creation under w3wp.exe.
      • Defender/AMSI: Check for detections such as Exploit:Script/SuspSignoutReq and Trojan:Win64/WebShell, and for AMSI block events in SharePoint ULS logs or the Defender operational log (EID 1116/1117).

    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 authentication in Microsoft Office SharePoint allows an unauthorized attacker to perform spoofing over a network.

    Source: CSA/SingCERT, NCSC NZ (CC BY 4.0), pwn.watch, certeu_advisory, Microsoft Security Update Guide, CISA KEV Catalog, cvelistv5, NVD (NIST), 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 – < 16.0.5508.1000
    • 16.0.5508.1000
    MicrosoftMicrosoft SharePoint Server 2019
    • 16.0.0 – < 16.0.10417.20027
    • 16.0.10417.20027
    MicrosoftMicrosoft SharePoint Server Subscription Edition
    • 16.0.0 – < 16.0.18526.20424
    • 16.0.18526.20424
    microsoftsharepoint_enterprise_server
    • 2016
    • —
    microsoftsharepoint_server
    • 2019
    • < 16.0.18526.20424
    • —
    • 16.0.18526.20424

    Vendors and products

    Weakness classes (CWE)

    • CWE-287Improper Authentication

      Class

      When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

      Entry at MITRE CWE-287

    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
    CSA/SingCERTCritical Vulnerabilities in Microsoft Sharepoint (opens in a new tab)CSA/SingCERTactively exploited
    NCSC NZCVE-2025-53770 and CVE-2025-53771 affecting Microsoft Sharepoint (opens in a new tab)NCSC NZactively exploited

    References & sources

    • Microsoft Security Update GuideMicrosoft SharePoint Server Spoofing VulnerabilityVendor advisory, Patch
    • microsoft.comDisrupting active exploitation of on-premises SharePoint vulnerabilitiesVendor advisory, pwn-watch
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2025-49706government-resource
    • pwn.watchpwn.watch: ToolShell: mass exploitation of on-prem SharePoint (CVE-2025-53770, CVE-2025-49704, CVE-2025-49706)pwn-watch
    • microsoft.comCustomer guidance for SharePoint vulnerability CVE-2025-53770pwn-watch
    • research.eye.securitySharePoint Under Siege: ToolShell Exploitpwn-watch
    • cisa.govUPDATE: Microsoft Releases Guidance on Exploitation of SharePoint Vulnerabilitiespwn-watch
    • enisa.europa.euJoint Statement on SharePoint vulnerabilitiespwn-watch
    • NVD (NIST)NVD: CVE-2025-53770pwn-watch
    • NVD (NIST)NVD: CVE-2025-49704pwn-watch
    • NVD (NIST)NVD: CVE-2025-49706pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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