CVE-2026-78509Network attack vector

Unauthenticated code execution via heap overflow

Published Sep 8, 2026 · Updated Sep 9, 2026

Heap-based buffer overflow in Microsoft Office Outlook allows remote attackers to execute code via network-delivered content. Microsoft identifies heap memory corruption but has not disclosed the parsing locus, malformed input, or missing bounds operation. No authentication or user interaction is required, and successful exploitation runs attacker-controlled code in the affected application context.

CVSS severity9.8
Critical
EPSS probability0.95%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in Microsoft Office Outlook allows remote attackers to execute code via network-delivered content. Microsoft identifies heap memory corruption but has not disclosed the parsing locus, malformed input, or missing bounds operation. No authentication or user interaction is required, and successful exploitation runs attacker-controlled code in the affected application context.

The record

CVE
CVE-2026-78509
Published
Sep 8, 2026
Updated
Sep 9, 2026
Vendor
Microsoft
Product
Microsoft Office LTSC for Mac 2024
Classifications
CWE-122, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=-

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Office LTSC for Mac 2024version=-
Microsoft · Microsoft Office 2019version=19.0.0 <16.0.10417.20207
Microsoft · Microsoft Office LTSC for Mac 2021version=-
Microsoft · Microsoft Office 365 for Macversion=-
Microsoft · Microsoft Office LTSC 2021version=16.0.1 <16.0.14334.20906
Microsoft · Microsoft Word 2016version=16.0.1 <16.0.5569.1000
Microsoft · Microsoft Office LTSC 2024version=16.0.0 <16.0.17932.20976
Microsoft · Microsoft 365 Apps for enterpriseversion=16.0.1 <16.0.20326.20138

Published CVSS scores

9.8MicrosoftCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-122Heap-based Buffer Overflow
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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