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Vulnerabilities

Vulnerability · CVE-2026-21258

Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.

Published Feb 10, 2026 · catalog updated Aug 19, 2026 · Microsoft Office Online Server

Last checked Nov 6, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-21258. EPSS is 0.63%. Act only if a listed version of Microsoft Office Online Server is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
Medium5.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.63%
Remediation
Version ranges on file
Affected products
vendor Microsoft Office Online Server 16.0.0.0 <16.0.10417.20097

Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor Microsoft Office Online Server 16.0.0.0 <16.0.10417.2009716.0.0.0 <16.0.10417.20097

How to fix CVE-2026-21258

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-21258. EPSS is 0.63%. Act only if a listed version of Microsoft Office Online Server is installed.

Which versions are affected?

Compare what you have installed with Microsoft Office Online Server 16.0.0.0 <16.0.10417.20097 16.0.0.0 <16.0.10417.20097. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.63%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Feb 10, 2026 · EUVD

    Detected

    Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.

  2. Aug 19, 2026 · EUVD

    Updated

    Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.

Sources

  • CVE.orgVulnerability recordCVE-2026-21258

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-21258

    30-day exploitation probability 0.63%

    first.org
  • EUVDVulnerability recordEUVD-2026-7356

    Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Nov 6, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 6, 2026
  • CVE.orgNov 4, 2026
  • EUVDNov 2, 2026