Summary
Impact: Information Disclosure. Microsoft rating: Important. Not known to be exploited — Exploitation Less Likely. Customer action: Required.
Details
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.
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.
Security updates
16.0.10417.20175 — https://support.microsoft.com/help/5002884
https — https://docs.microsoft.com/en-us/officeupdates/microsoft365-apps-security-updates
16.111.26071215 — https://go.microsoft.com/fwlink/p/?linkid=831049
16.0.5561.1001 — https://support.microsoft.com/help/5002877
16.111.26071215 — https://www.microsoft.com/en-us/microsoft-365/mac/microsoft-365-for-mac?msockid=35f9adb0e74b61392038b90de6fe608c
Vulnerabilities 1
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Medium 5.5
Microsoft Excel Information Disclosure Vulnerability
Untrusted pointer dereference 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-2026-55138 Microsoft Excel Information Disclosure Vulnerability - HTML
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55138
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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