Code execution via integer underflow
Published Jul 14, 2026 · Updated Jul 14, 2026
Integer underflow in Microsoft Excel allows attackers to execute code locally after a user opens a malicious Office file. Microsoft identifies a resulting heap buffer overflow but has not disclosed the affected parser or the arithmetic operation that underflows. Exploitation requires user interaction, and successful code runs in the security context of the user who opens the file.
Summary
What happened
Integer underflow in Microsoft Excel allows attackers to execute code locally after a user opens a malicious Office file. Microsoft identifies a resulting heap buffer overflow but has not disclosed the affected parser or the arithmetic operation that underflows. Exploitation requires user interaction, and successful code runs in the security context of the user who opens the file.
The record
- CVE
- CVE-2026-55039
- Published
- Jul 14, 2026
- Updated
- Jul 14, 2026
- Vendor
- Microsoft
- Product
- Microsoft Office LTSC for Mac 2024
- Classifications
- CWE-122, CWE-191, T1203, T1204.002
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 14, 2026CVE publishedPublication date reported by the CVE source.
- Jul 14, 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.
- Affected versionversion=16.0.0 <16.111.26071215
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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