Summary
Impact: Information Disclosure. Microsoft rating: Important. Not known to be exploited — Exploitation Less Likely. Customer action: Required.
Details
According to the CVSS metric, user interaction is required (UI:R). What interaction would the user have to do?
An attacker must send a user a malicious Office file and convince them to open it.
What type of information could be disclosed by this vulnerability?
An attacker who successfully exploited this vulnerability could potentially read small portions of heap memory.
Is the Preview Pane an attack vector for this vulnerability?
No, the Preview Pane is not an attack vector.
Security updates
16.0.10417.20097 — https://support.microsoft.com/help/5002835
https — https://docs.microsoft.com/en-us/officeupdates/microsoft365-apps-security-updates
16.106.26020821 — https://go.microsoft.com/fwlink/p/?linkid=831049
16.0.5539.1002 — https://support.microsoft.com/help/5002837
Vulnerabilities 1
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Medium 5.5
Microsoft Excel Information Disclosure Vulnerability
Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.
Revision history
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#1
Information published.
References
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CVE-2026-21258 Microsoft Excel Information Disclosure Vulnerability - HTML
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21258
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Microsoft Exploitability Index
https://www.microsoft.com/en-us/msrc/exploitability-index?rtc=1
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Microsoft Support Lifecycle
https://support.microsoft.com/lifecycle
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Common Vulnerability Scoring System
https://www.first.org/cvss