CVE-2026-64903

Code execution via integer overflow

Published Aug 11, 2026 · Updated Aug 25, 2026

Integer overflow in Microsoft Office before the August 2026 fixes allows attackers to execute code locally via a crafted Office file. Microsoft has disclosed only that Office mishandles an arithmetic operation, and the CNA's paired CWE-190 and CWE-122 mappings indicate a wrapped size calculation can lead to an undersized heap buffer and memory corruption. Successful exploitation depends on getting a user to open the malicious file; third-party Patch Tuesday analyses also report Preview Pane reachability for this CVE, but Microsoft has not named the affected parser, component, or file format.

CVSS severityUnavailable
Unscored
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in Microsoft Office before the August 2026 fixes allows attackers to execute code locally via a crafted Office file. Microsoft has disclosed only that Office mishandles an arithmetic operation, and the CNA's paired CWE-190 and CWE-122 mappings indicate a wrapped size calculation can lead to an undersized heap buffer and memory corruption. Successful exploitation depends on getting a user to open the malicious file; third-party Patch Tuesday analyses also report Preview Pane reachability for this CVE, but Microsoft has not named the affected parser, component, or file format.

The record

CVE
CVE-2026-64903
Published
Aug 11, 2026
Updated
Aug 25, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-190, CWE-122, T1203, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 11, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 25, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8MicrosoftCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
CWE-122Heap-based Buffer Overflow
T1203Exploitation for Client Execution
T1204.002User Execution: Malicious File

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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