CriticalCVE-2026-124194

    Microsoft Outlook Spoofing Vulnerability (CVE-2026-124194)

    Published Last modified In CISA KEV since Sources: Msrc Update Guide, CVE.org, EUVD, JPCERT/CC, BSI

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    What is affected, what to do

    Product ui does not warn user of unsafe actions in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.

    The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Office LTSC 2021 to version 16.0.14334.21048, Microsoft Office LTSC 2024 to version 16.0.17932.21140. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft 365 Apps for Enterprise gte 16.0.1..*
    • Microsoft Office LTSC 2021 lt 16.0.1..16.0.14334.21048
    • Microsoft Office LTSC 2024 lt 16.0.0..16.0.17932.21140
    Fixed in
    • Microsoft Office LTSC 2021 16.0.14334.21048
    • Microsoft Office LTSC 2024 16.0.17932.21140

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

    Metrics

    6.5

    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: Msrc Update Guide, CVE.org, EUVD, JPCERT/CC, BSI

    1.6 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 76.4

    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
    209.26 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), CIRCL Sightings, Cisco Talos, HKCERT 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
    1.6 %
    Moderate — model estimates 1-10% 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
    76.4
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    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
    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 9 November 2026
    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-356

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is network-reachable without authentication. It needs only a user interacting with a crafted message, and its impact is concentrated on confidentiality. In practice, Outlook spoofing bugs of this kind are used to harvest NTLM credentials for relay or offline cracking, giving attackers a foothold into Active Directory. CISA lists no known ransomware use. Even so, organisations with a large Outlook population, incomplete SMB egress filtering or no NTLM restrictions should treat this as a high-priority patch within their emergency SLA. Where outbound SMB/WebDAV is already strictly blocked, residual risk drops considerably.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Push Office updates now: Microsoft Office LTSC 2021 to build 16.0.14334.21048 or later, Microsoft Office LTSC 2024 to build 16.0.17932.21140 or later. For Microsoft 365 Apps for Enterprise a patch is available from the vendor. Look up the fixed build per update channel (Current, Monthly Enterprise, Semi-Annual) in the Microsoft Security Update Guide.
      • Inventory patch state via Intune, ConfigMgr or Defender Vulnerability Management (query outlook.exe file version). Prioritise Semi-Annual channel devices and VDI/Citrix golden images, as these usually lag behind.
      • Block or verify the existing block of outbound SMB (TCP 445/139) and WebDAV (TCP 80/443 via the WebClient service) from clients to the internet at the perimeter. This "no warning on unsafe action" class of Outlook flaw is typically abused to coerce NTLM authentication to attacker-controlled hosts.
      • Add privileged accounts (Domain Admins, Tier 0/1, help desk) to the Protected Users group. This disables NTLM for them and limits the blast radius of a leaked hash.
      • Hunt mailboxes for recent suspicious messages, especially HTML mail containing file://, UNC (\\host\share) or unusual URI-scheme links. Purge hits tenant-wide via Defender for Office soft delete or Content Search.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Restrict egress so clients can reach only designated internal file servers over SMB. Also log and drop client-VLAN traffic on TCP 445 to non-RFC1918 destinations.
      • IAM / authentication: Set the GPO "Network security: Restrict NTLM: Outgoing NTLM traffic to remote servers" to "Audit all" first, then to "Deny all" with an exception list. Enforce SMB signing and Extended Protection for Authentication on your own servers to frustrate relay.
      • Endpoint hardening: Disable the WebClient service where WebDAV is not needed (sc config WebClient start= disabled). Also enable the ASR rule "Block Office communication application from creating child processes" in block mode.
      • Mail gateway: Create a transport rule or Defender for Office policy that quarantines messages carrying file: URIs or UNC paths in the HTML body or in calendar items (reminder-sound properties). Enable Safe Links and Safe Attachments for all recipients.
      • Configuration: For high-risk groups (finance, executives), temporarily disable the Outlook reading pane and automatic download of external content via policy until the rollout is complete.

    3. Runbook step 3

      Detection rules

      • EDR/MDE: DeviceNetworkEvents | where InitiatingProcessFileName =~ "outlook.exe" and RemotePort in (445,139) and RemoteIPType == "Public". Treat any hit as high-confidence suspicious.
      • Sysmon EID 3: Use a Sigma shape with Image|endswith: '\OUTLOOK.EXE', DestinationPort: 445 and DestinationIp outside private ranges. Additionally catch WebClient svchost.exe issuing outbound HTTP PROPFIND right after Outlook activity.
      • NTLM auditing: In the Microsoft-Windows-NTLM/Operational channel, Event 8001 (outgoing NTLM auth) with an external target server name, plus Windows Firewall Event 5156 (TCP 445 outbound to external), directly indicate hash leakage.
      • Network telemetry: Treat Zeek ntlm.log/smb_mapping.log entries or a Suricata alert smb $HOME_NET any -> $EXTERNAL_NET any as indicators. Correlate them with subsequent 4624 logons (LogonType 3, NTLM) from unfamiliar source IPs, which suggest relay or cracked hashes.
      • Mail telemetry: EmailUrlInfo | where Url startswith "file:" or Url contains "\\\\", joined to EmailEvents for delivered messages from external senders.

    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

    Product ui does not warn user of unsafe actions in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.

    Source: Microsoft Security Update Guide, cvelistv5, ENISA EUVD, NVD (NIST), JPCERT/CC, CISA KEV Catalog, CVE.org (MITRE), BSI CSAF, BSI WID Portal

    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 365 Apps for Enterprise
    • ≥ 16.0.1
    • —
    MicrosoftMicrosoft Office LTSC 2021
    • 16.0.1 – < 16.0.14334.21048
    • 16.0.14334.21048
    MicrosoftMicrosoft Office LTSC 2024
    • 16.0.0 – < 16.0.17932.21140
    • 16.0.17932.21140
    microsoft365_apps
    • —
    • —
    microsoftoffice_2021
    • —
    • —
    microsoftoffice_2024
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-356Product UI does not Warn User of Unsafe Actions

      Base

      The product's user interface does not warn the user before undertaking an unsafe action on behalf of that user. This makes it easier for attackers to trick users into inflicting damage to their system.

      Entry at MITRE CWE-356

    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
    HKCERTMicrosoft Monthly Security Update (November 2026) (opens in a new tab)HKCERTactively exploited

    References & sources

    • Microsoft Security Update GuideMicrosoft Outlook Spoofing Vulnerabilityeuvd, Vendor advisory, Patch, Vendor advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-1241…US government resource, government-resource, euvd
    • NVD (NIST)vuln/detail/CVE-2026-124194euvd
    • JPCERT/CCJPCERT/CC JPCERT-AT-2026-0035: Microsoft Releases November 2026 Security Updatesjpcert

    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).

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: active, automatable: no

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentremoved
      {"id":"CVE-2026-124194","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-11-10T19:50:07.348899Z"}
      —
      SSVC assessmentadded
      —
      {"id":"CVE-2026-124194","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-11-09T00:00:00+00:00"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Initial analysis by NVDNVD

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Product configurationadded
      —
      OR *cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x64:* *cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x86:* *cpe:2.3:a:microsoft:office_2021:-:*:*:*:ltsc:-:x64:* *cpe:2.3:a:microsoft:office_2021:-:*:*:*:ltsc:-:x86:* *cpe:2.3:a:microsoft:office_2024:-:*:*:*:ltsc:-:x64:* *cpe:2.3:a:microsoft:office_2024:-:*:*:*:ltsc:-:x86:*
      Reference typeadded
      —
      Microsoft Corporation: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-124194 Types: Vendor Advisory
      Reference typeadded
      —
      CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-124194 Types: US Government Resource

      Source identifier: nvd@nist.gov

    3. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: active, automatable: no

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-124194
      SSVC assessmentadded
      —
      {"id":"CVE-2026-124194","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-11-10T19:50:07.348899Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    4. CISA KEV entry updated9119a7d8…

      4 individual changes: Date Added, Due Date, Required Action, Vulnerability Name

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Date Addedadded
      —
      2026-11-10
      Due Dateadded
      —
      2026-11-10
      Required Actionadded
      —
      2026-11-10
      Vulnerability Nameadded
      —
      2026-11-10

      Source identifier: 9119a7d8-5eab-497f-8521-727c672e3725

    5. ReceivedMicrosoft

      CVSS V3.1: AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

      Weakness type: CWE-356

      Description added or changed

      Show 5 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      Product ui does not warn user of unsafe actions in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
      Weakness type (CWE)added
      —
      CWE-356
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/124xxx/CVE-2026-124194.json">CVE-2026-124194</a>
      Referenceadded
      —
      https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-124194

      Source identifier: secure@microsoft.com

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