VulnTideExploited vulnerabilities, by vendor. Data as of .
Not in CISA KEVPublished CVSS 9.8 criticalEPSS 1% probability of exploitation in 30 days
Microsoft

CVE-2026-78509: Microsoft Office Outlook Remote Code Execution Vulnerability

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of . If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?
1%

EPSS score, percentile 62 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?
9.8 Critical

CVSS v3.1 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (1)

Which versions are affected?

Affected

  • from 16.0.1 to before 16.0.20326.20138
  • from 19.0.0 to before 16.0.10417.20207
  • from 1.0.0 to before 16.113.26091433
  • from 16.0.1 to before 16.0.14334.20906
  • from 16.0.0 to before 16.0.17932.20976
  • from 16.0.1 to before 16.113.26091433

and 2 more in the table below

Versions by product

Source: CISA KEV 2026.10.29, as of ; FIRST EPSS, as of ; CVE List, as of . About the data.

What to do

Advisories and patches

This summary is based on the CVE record as of . Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Microsoft Microsoft 365 Apps for Enterprise
StatusVersions
Affectedfrom 16.0.1 to before 16.0.20326.20138
Microsoft Microsoft Office 2019
StatusVersions
Affectedfrom 19.0.0 to before 16.0.10417.20207
Microsoft Microsoft Office 365 for Mac
StatusVersions
Affectedfrom 1.0.0 to before 16.113.26091433
Microsoft Microsoft Office LTSC 2021
StatusVersions
Affectedfrom 16.0.1 to before 16.0.14334.20906
Microsoft Microsoft Office LTSC 2024
StatusVersions
Affectedfrom 16.0.0 to before 16.0.17932.20976
Microsoft Microsoft Office LTSC for Mac 2021
StatusVersions
Affectedfrom 16.0.1 to before 16.113.26091433
Microsoft Microsoft Office LTSC for Mac 2024
StatusVersions
Affectedfrom 16.0.0 to before 16.113.26091433
Microsoft Microsoft Word 2016
StatusVersions
Affectedfrom 16.0.1 to before 16.0.5569.1000

Source: CVE List, as of . About the data.

About this vulnerability

Heap-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.

Summary: CVE record, as of .

  • CISA has not added CVE-2026-78509 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
  • The CVE record was published on 8 Sep 2026.
  • The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), given by its CNA.
  • FIRST's EPSS model puts the probability of exploitation in the next 30 days at 1% (percentile 62), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
  • CISA's SSVC assessment in the CVE record: exploitation none, automatable yes, technical impact total.

Source: CISA KEV 2026.10.29, as of ; CVE List, as of ; FIRST EPSS, as of . About the data.

Description

Microsoft Office Outlook Remote Code Execution Vulnerability

Heap-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.

Source: CVE List, as of . About the data.

Weakness

CWE-122
  • CWE-122: Heap-based Buffer Overflow

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record.

Timeline

DateEvent
CVE record published
CVE record last updated

Known exploited Microsoft vulnerabilities

  • CVE-2026-96951: Microsoft Windows Command Injection Vulnerability (added )
  • CVE-2026-65660: Microsoft SharePoint Code Injection Vulnerability (added )
  • CVE-2026-81963: Microsoft Windows Link Following Vulnerability (added )
  • CVE-2026-85880: Microsoft Windows Heap-Based Buffer Overflow Vulnerability (added )
  • CVE-2019-1068: Microsoft SQL Server Remote Code Execution Vulnerability (added )