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Office CVE-2026-21258

MEDIUM
Improper Input Validation (CWE-20)
2026-02-10 secure@microsoft.com
Microsoft 365 Apps Excel Office Office Long Term Servicing Channel Office Online Server
5.5
CVSS 3.1 · NVD
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Vulnerability Assessment

Weakness
CWE
CWE-20
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V2 - Validation and Business Logic Input validation, allowlisting
Impact

CVSS 5.5 (MEDIUM). Attack vector: Local. Complexity: Low. Privileges required: None. User interaction: Required. Exploitation no authentication required. Exploitable via local access.
Exploit ScenarioDerived

An attacker without authentication could exploit this vulnerability to compromise the affected system.
This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

Information disclosure in Microsoft Excel allows local attackers with user interaction to read sensitive data through improper input validation in Office 365 Apps and Long Term Servicing Channel. An attacker must socially engineer a user into opening a specially crafted file to trigger the vulnerability. No patch is currently available for this medium-severity issue.

Earlier versions of this analysis (1)
v1 Mar 12, 2026 - 22:02 CVSS 5.5

Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally. [CVSS 5.5 MEDIUM]

RemediationAI

Monitor vendor advisories for a patch.

Affected Packages

microsoft 365_apps_for_enterprise_https_aka_ms_officesecurityreleases fix: Microsoft 365 Apps for Enterprise for 32-bit Systems https://aka.ms/OfficeSecurityReleases, Microsoft 365 Apps for Enterprise for 64-bit Systems https://aka.ms/OfficeSecurityReleases
microsoft excel_2016_32_bit_edition_16_0_5539_1002 fix: Microsoft Excel 2016 (32-bit edition) 16.0.5539.1002
microsoft excel_2016_64_bit_edition_16_0_5539_1002 fix: Microsoft Excel 2016 (64-bit edition) 16.0.5539.1002
microsoft office_2019_editions_https_aka_ms_officesecurityreleases fix: Microsoft Office 2019 for 32-bit editions https://aka.ms/OfficeSecurityReleases, Microsoft Office 2019 for 64-bit editions https://aka.ms/OfficeSecurityReleases
microsoft office_ltsc_2021_editions_https_aka_ms_officesecurityreleases fix: Microsoft Office LTSC 2021 for 32-bit editions https://aka.ms/OfficeSecurityReleases, Microsoft Office LTSC 2021 for 64-bit editions https://aka.ms/OfficeSecurityReleases
microsoft office_ltsc_2024_editions_https_aka_ms_officesecurityreleases fix: Microsoft Office LTSC 2024 for 32-bit editions https://aka.ms/OfficeSecurityReleases, Microsoft Office LTSC 2024 for 64-bit editions https://aka.ms/OfficeSecurityReleases
microsoft office_ltsc_for_mac_2021_16_106_26020821 fix: Microsoft Office LTSC for Mac 2021 16.106.26020821
microsoft office_ltsc_for_mac_2024_16_106_26020821 fix: Microsoft Office LTSC for Mac 2024 16.106.26020821
microsoft office_online_server_16_0_10417_20097 fix: Office Online Server 16.0.10417.20097

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 9 packages in microsoft

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Technical ContextAI · show details

Classified as CWE-20 (Improper Input Validation). Affects 365 Apps. Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.

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  • Exploit and PoC references, threat intelligence from 22 sources
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Severity by source

NVD PRIMARY 5.5 MEDIUM
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

DescriptionCVE.org

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

Executive ViewAI

Why It Matters

Organizations using Improper input validation in Microsoft Office Excel should be aware of moderate risk from CVE-2026-21258, a input validation vulnerability rated CVSS 5.5. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and monitor for exploitation.

Business Impact: Low
Compensating Controls

Apply vendor patch. If patching is delayed: deploy WAF rules, restrict network access, enable logging.

Threat Intelligence Overview

EPSS Score
0.0%
Top 87% exploitable
Data Quality
3 sources
Confidence: Low
NVD CVE.org EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Defer
Exploitation· derived
None
System Exposure· derived
Small
Automatable· derived
No
Human Impact
Low

Priority Score

28
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +28
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Affected Products (CPE)CVE.org

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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References

Advisories & patches
ADVISORY https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21258

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