Vulnerability-Lookup

MSRC_CVE-2026-21509

Vulnerability from csaf_microsoft - Published: 2026-01-13 08:00 - Updated: 2026-01-29 08:00

Summary

Microsoft Office Security Feature Bypass Vulnerability

Severity

Important

Notes

Additional Resources: To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle

Disclaimer: The information provided in the Microsoft Knowledge Base is provided \"as is\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Customer Action: Required. The vulnerability documented by this CVE requires customer action to resolve.

CVE-2026-21509

7.8 (High)


                
                  CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

CWE-807 - Reliance on Untrusted Inputs in a Security Decision

Affected products

Fixed 10 products

Product	Identifier	Version	Remediation
Microsoft Office 2016 (32-bit edition) 16.0.5539.1001 Microsoft Office 2016 (32-bit edition)		16.0.5539.1001
Microsoft Office 2016 (64-bit edition) 16.0.5539.1001 Microsoft Office 2016 (64-bit edition)		16.0.5539.1001
Microsoft Office 2019 for 32-bit editions 16.0.10417.20095 Microsoft Office 2019 for 32-bit editions		16.0.10417.20095
Microsoft Office 2019 for 64-bit editions 16.0.10417.20095 Microsoft Office 2019 for 64-bit editions		16.0.10417.20095
Microsoft 365 Apps for Enterprise for 32-bit Systems https://aka.ms/OfficeSecurityReleases Microsoft 365 Apps for Enterprise for 32-bit Systems		https://aka.ms/OfficeSecurityReleases
Microsoft 365 Apps for Enterprise for 64-bit Systems https://aka.ms/OfficeSecurityReleases Microsoft 365 Apps for Enterprise for 64-bit Systems		https://aka.ms/OfficeSecurityReleases
Microsoft Office LTSC 2021 for 64-bit editions https://aka.ms/OfficeSecurityReleases Microsoft Office LTSC 2021 for 64-bit editions		https://aka.ms/OfficeSecurityReleases
Microsoft Office LTSC 2021 for 32-bit editions https://aka.ms/OfficeSecurityReleases Microsoft Office LTSC 2021 for 32-bit editions		https://aka.ms/OfficeSecurityReleases
Microsoft Office LTSC 2024 for 32-bit editions https://aka.ms/OfficeSecurityReleases Microsoft Office LTSC 2024 for 32-bit editions		https://aka.ms/OfficeSecurityReleases
Microsoft Office LTSC 2024 for 64-bit editions https://aka.ms/OfficeSecurityReleases Microsoft Office LTSC 2024 for 64-bit editions		https://aka.ms/OfficeSecurityReleases

Known affected 10 products

Product	Version	Remediation
Microsoft Office LTSC 2024 for 64-bit editions <https://aka.ms/OfficeSecurityReleases Microsoft Office LTSC 2024 for 64-bit editions	<https://aka.ms/OfficeSecurityReleases	Vendor Fix fix
Microsoft Office LTSC 2024 for 32-bit editions <https://aka.ms/OfficeSecurityReleases Microsoft Office LTSC 2024 for 32-bit editions	<https://aka.ms/OfficeSecurityReleases	Vendor Fix fix
Microsoft Office LTSC 2021 for 32-bit editions <https://aka.ms/OfficeSecurityReleases Microsoft Office LTSC 2021 for 32-bit editions	<https://aka.ms/OfficeSecurityReleases	Vendor Fix fix
Microsoft Office LTSC 2021 for 64-bit editions <https://aka.ms/OfficeSecurityReleases Microsoft Office LTSC 2021 for 64-bit editions	<https://aka.ms/OfficeSecurityReleases	Vendor Fix fix
Microsoft 365 Apps for Enterprise for 64-bit Systems <https://aka.ms/OfficeSecurityReleases Microsoft 365 Apps for Enterprise for 64-bit Systems	<https://aka.ms/OfficeSecurityReleases	Vendor Fix fix
Microsoft 365 Apps for Enterprise for 32-bit Systems <https://aka.ms/OfficeSecurityReleases Microsoft 365 Apps for Enterprise for 32-bit Systems	<https://aka.ms/OfficeSecurityReleases	Vendor Fix fix
Microsoft Office 2019 for 64-bit editions <16.0.10417.20095 Microsoft Office 2019 for 64-bit editions	<16.0.10417.20095	Vendor Fix fix
Microsoft Office 2019 for 32-bit editions <16.0.10417.20095 Microsoft Office 2019 for 32-bit editions	<16.0.10417.20095	Vendor Fix fix
Microsoft Office 2016 (64-bit edition) <16.0.5539.1001 Microsoft Office 2016 (64-bit edition)	<16.0.5539.1001	Vendor Fix fix
Microsoft Office 2016 (32-bit edition) <16.0.5539.1001 Microsoft Office 2016 (32-bit edition)	<16.0.5539.1001	Vendor Fix fix

Threats

Impact Security Feature Bypass

Exploit Status Publicly Disclosed:No;Exploited:Yes;Latest Software Release:Exploitation Detected

References

7 references

URL	Category
https://msrc.microsoft.com/update-guide/vulnerabi…	self
https://msrc.microsoft.com/csaf/advisories/2026/m…	self
https://www.microsoft.com/en-us/msrc/exploitabili…	external
https://support.microsoft.com/lifecycle	external
https://www.first.org/cvss	external
https://msrc.microsoft.com/update-guide/vulnerabi…	self
https://msrc.microsoft.com/csaf/advisories/2026/m…	self

Acknowledgments

Microsoft Threat Intelligence Center (MSTIC), Microsoft Security Response Center (MSRC), and Office Product Group Security Team

Google Threat Intelligence Group

JSON

To clipboard

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    "acknowledgments": [
      {
        "names": [
          "Microsoft Threat Intelligence Center (MSTIC), Microsoft Security Response Center (MSRC), and Office Product Group Security Team"
        ]
      },
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        "names": [
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        "text": "To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle",
        "title": "Additional Resources"
      },
      {
        "category": "legal_disclaimer",
        "text": "The information provided in the Microsoft Knowledge Base is provided \\\"as is\\\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.",
        "title": "Disclaimer"
      },
      {
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        "text": "Required. The vulnerability documented by this CVE requires customer action to resolve.",
        "title": "Customer Action"
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    "publisher": {
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      "contact_details": "secure@microsoft.com",
      "name": "Microsoft Security Response Center",
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    "references": [
      {
        "category": "self",
        "summary": "CVE-2026-21509 Microsoft Office Security Feature Bypass Vulnerability - HTML",
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509"
      },
      {
        "category": "self",
        "summary": "CVE-2026-21509 Microsoft Office Security Feature Bypass Vulnerability - CSAF",
        "url": "https://msrc.microsoft.com/csaf/advisories/2026/msrc_cve-2026-21509.json"
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    "title": "Microsoft Office Security Feature Bypass Vulnerability",
    "tracking": {
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        "date": "2026-02-13T20:39:54.891Z",
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          "number": "1",
          "summary": "Information published."
        },
        {
          "date": "2026-01-26T08:00:00.000Z",
          "legacy_version": "1.1",
          "number": "2",
          "summary": "Corrected CVSS score. This is an informational change only."
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          "date": "2026-01-26T08:00:00.000Z",
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          "number": "3",
          "summary": "The following revisions have been made: 1) Microsoft is announcing the availability of the security updates for Microsoft Office 2016 and 2019. Customers running these versions of Office should install the update for their product to be protected from this vulnerability. Customers whose systems are configured to receive automatic updates do not need to take any further action. 2) Updated FAQ and Mitigations."
        },
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          "date": "2026-01-26T08:00:00.000Z",
          "legacy_version": "2.1",
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        },
        {
          "date": "2026-01-27T08:00:00.000Z",
          "legacy_version": "2.2",
          "number": "5",
          "summary": "Updated FAQ information. This is an informational change only."
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        {
          "date": "2026-01-28T08:00:00.000Z",
          "legacy_version": "2.3",
          "number": "6",
          "summary": "Acknowledgement added. This is an informational change only."
        },
        {
          "date": "2026-01-29T08:00:00.000Z",
          "legacy_version": "2.4",
          "number": "7",
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        }
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      "status": "final",
      "version": "7"
    }
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              "product_id": "4"
            }
          },
          {
            "category": "product_version",
            "name": "https://aka.ms/OfficeSecurityReleases",
            "product": {
              "name": "Microsoft Office LTSC 2021 for 64-bit editions https://aka.ms/OfficeSecurityReleases",
              "product_id": "11952"
            }
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              "product_id": "2"
            }
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            "name": "https://aka.ms/OfficeSecurityReleases",
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              "product_id": "10"
            }
          },
          {
            "category": "product_version",
            "name": "16.0.5539.1001",
            "product": {
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              "product_id": "10753"
            }
          }
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        "name": "Microsoft Office 2016 (32-bit edition)"
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            "product": {
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              "product_id": "9"
            }
          },
          {
            "category": "product_version",
            "name": "16.0.5539.1001",
            "product": {
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            }
          }
        ],
        "category": "product_name",
        "name": "Microsoft Office 2016 (64-bit edition)"
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  },
  "vulnerabilities": [
    {
      "cve": "CVE-2026-21509",
      "cwe": {
        "id": "CWE-807",
        "name": "Reliance on Untrusted Inputs in a Security Decision"
      },
      "notes": [
        {
          "category": "general",
          "text": "Microsoft",
          "title": "Assigning CNA"
        },
        {
          "category": "faq",
          "text": "An attacker must send a user a malicious Office file and convince them to open it.",
          "title": "According to the CVSS metric, user interaction is required (UI:R). What interaction would the user have to do?"
        },
        {
          "category": "faq",
          "text": "Yes. As of January 26, 2026, the security update for Microsoft Office 2016 and 2019 is available. Customers running Microsoft Office 2016 and 2019 should ensure the update is installed to be protected from this vulnerability.",
          "title": "Are the updates for Microsoft Office 2016 and 2019 currently available?"
        },
        {
          "category": "faq",
          "text": "On January 26 2026, Microsoft released build numbers for Office 2016 16.0.5539.1001 and Office 2019 16.0.10417.20095 to address this vulnerability.\nTo see what version you have installed:\nIn a document click the File tab.\nClick Account in the left hand pane.\nClick About . The top line of the About dialog box will display the Build number.",
          "title": "How do I know what version of Office 2016 and 2019 I am running?"
        },
        {
          "category": "faq",
          "text": "This update addresses a vulnerability that bypasses OLE mitigations in Microsoft 365 and Microsoft Office which protect users from vulnerable COM/OLE controls.",
          "title": "What kind of security feature could be bypassed by successfully exploiting this vulnerability?"
        },
        {
          "category": "faq",
          "text": "No, the Preview Pane is not an attack vector.",
          "title": "Is the Preview Pane an attack vector for this vulnerability?"
        }
      ],
      "product_status": {
        "fixed": [
          "10753",
          "10754",
          "11573",
          "11574",
          "11762",
          "11763",
          "11952",
          "11953",
          "12420",
          "12421"
        ],
        "known_affected": [
          "1",
          "2",
          "3",
          "4",
          "5",
          "6",
          "7",
          "8",
          "9",
          "10"
        ]
      },
      "references": [
        {
          "category": "self",
          "summary": "CVE-2026-21509 Microsoft Office Security Feature Bypass Vulnerability - HTML",
          "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509"
        },
        {
          "category": "self",
          "summary": "CVE-2026-21509 Microsoft Office Security Feature Bypass Vulnerability - CSAF",
          "url": "https://msrc.microsoft.com/csaf/advisories/2026/msrc_cve-2026-21509.json"
        }
      ],
      "remediations": [
        {
          "category": "vendor_fix",
          "date": "2026-01-26T08:00:00.000Z",
          "details": "16.0.10417.20095:Security Update:https://learn.microsoft.com/en-us/officeupdates/update-history-office-2019",
          "product_ids": [
            "8",
            "7"
          ],
          "url": "https://learn.microsoft.com/en-us/officeupdates/update-history-office-2019"
        },
        {
          "category": "vendor_fix",
          "date": "2026-01-26T08:00:00.000Z",
          "details": "https://aka.ms/OfficeSecurityReleases:Security Update:https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates",
          "product_ids": [
            "6",
            "5",
            "4",
            "3",
            "2",
            "1"
          ],
          "url": "https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates"
        },
        {
          "category": "vendor_fix",
          "date": "2026-01-26T08:00:00.000Z",
          "details": "16.0.5539.1001:Security Update:https://support.microsoft.com/help/5002713",
          "product_ids": [
            "10",
            "9"
          ],
          "url": "https://support.microsoft.com/help/5002713"
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "environmentalsScore": 0.0,
            "exploitCodeMaturity": "FUNCTIONAL",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "remediationLevel": "OFFICIAL_FIX",
            "reportConfidence": "CONFIRMED",
            "scope": "UNCHANGED",
            "temporalScore": 7.2,
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C",
            "version": "3.1"
          },
          "products": [
            "1",
            "2",
            "3",
            "4",
            "5",
            "6",
            "7",
            "8",
            "9",
            "10"
          ]
        }
      ],
      "threats": [
        {
          "category": "impact",
          "details": "Security Feature Bypass"
        },
        {
          "category": "exploit_status",
          "details": "Publicly Disclosed:No;Exploited:Yes;Latest Software Release:Exploitation Detected"
        }
      ],
      "title": "Microsoft Office Security Feature Bypass Vulnerability"
    }
  ]
}

CVE-2026-21509 (GCVE-0-2026-21509)

Vulnerability from cvelistv5 – Published: 2026-01-26 17:06 – Updated: 2026-07-30 20:47

Title

Microsoft Office Security Feature Bypass Vulnerability

Summary

Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

SSVC

Exploitation: active Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-01-26 00:00 UTC

CWE

CWE-807 - Reliance on Untrusted Inputs in a Security Decision

Assigner

microsoft CNA under the mitre root

CNA scorecard B 82/100 over 3963 records in the last 180 days details

References

4 references

URL	Tags
https://msrc.microsoft.com/update-guide/vulnerabi…	vendor-advisorypatch
https://www.cisa.gov/known-exploited-vulnerabilit…	government-resource
https://www.vicarius.io/vsociety/posts/cve-2026-2…
https://www.vicarius.io/vsociety/posts/cve-2026-2…

Impacted products

5 products

Vendor	Product	Version
Microsoft	Microsoft 365 Apps for Enterprise	Affected: 16.0.1 , < https://aka.ms/OfficeSecurityReleases (custom)
Microsoft	Microsoft Office 2016	Affected: 16.0.0 , < 16.0.5539.1001 (custom)
Microsoft	Microsoft Office 2019	Affected: 19.0.0 , < 16.0.10417.20095 (custom)
Microsoft	Microsoft Office LTSC 2021	Affected: 16.0.1 , < https://aka.ms/OfficeSecurityReleases (custom)
Microsoft	Microsoft Office LTSC 2024	Affected: 16.0.0 , < https://aka.ms/OfficeSecurityReleases (custom)

Date Public

2026-01-26 16:00

Show details on NVD website

JSON

To clipboard

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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

Order JSON

How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

Publication & reservation Sightings KEV catalogs Other timestamps

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

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