How severe is CVE-2026-21258?

CVE-2026-21258 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2026-21258 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21258?

CVE-2026-21258 primarily affects Microsoft 365 Apps. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-21258?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-21258 have an EU (EUVD) identifier?

Yes. CVE-2026-21258 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7356.

When was CVE-2026-21258 published?

CVE-2026-21258 was published on 2026-02-10 and last updated on 2026-06-17.

CVE-2026-21258

CVE-2026-21258 is a medium-severity vulnerability in Microsoft 365 Apps with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Medium (CVSS 3.x base score 5.5)
EPSS exploit prediction: 1% (44th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-7356
Weakness: CWE-20
Affected product: Microsoft 365 Apps
Published: 2026-02-10
Last modified: 2026-06-17

Description

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

Frequently asked questions

What is CVE-2026-21258?: Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.
How severe is CVE-2026-21258?: CVE-2026-21258 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2026-21258 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21258?: CVE-2026-21258 primarily affects Microsoft 365 Apps. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-21258?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-21258 have an EU (EUVD) identifier?: Yes. CVE-2026-21258 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7356.
When was CVE-2026-21258 published?: CVE-2026-21258 was published on 2026-02-10 and last updated on 2026-06-17.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21258

Affected products (13)

cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x64:*
cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x86:*
cpe:2.3:a:microsoft:excel:2016:*:*:*:*:*:x64:*
cpe:2.3:a:microsoft:excel:2016:*:*:*:*:*:x86:*
cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x64:*
cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x86:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x64:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x86:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:macos:*:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x64:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x86:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:macos:*:*
cpe:2.3:a:microsoft:office_online_server:*:*:*:*:*:*:*:*

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