Vulnerability report

Trusted Third Party Report Confirmed Confidence In CISA KEV

CVE-2021-38646

Microsoft 365 Apps for Enterprise Remote Code Execution

Microsoft 365 Apps for Enterprise · affected before https://aka.ms/OfficeSecurityReleases

Watch CVE-2021-38646 Browse KEV feed
Severity
CVSS 7.8 · High
Confidence
Confirmed
Exploit status
Trusted Third Party Report
EPSS
8.0%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2021-38646 is an unauthenticated vulnerability affecting Microsoft 365 Apps for Enterprise, Microsoft Office 2013 Service Pack 1, Microsoft Office 2016, Microsoft Office 2019.

Have exploitation attempts been observed?

Yes. Exploitation attempts have been reported for this vulnerability. Previdian lists it as a known exploited vulnerability. Listed in CISA KEV. Also reported by third-party sources. Confidence is confirmed.

Who is affected?

Affected products include Microsoft 365 Apps for Enterprise and 3 other products, including affected before https://aka.ms/OfficeSecurityReleases, affected before 5381.1000, and affected before 5215.1000.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability

Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability

Microsoft Affected
Microsoft 365 Apps for Enterprise
Before https://aka.ms/OfficeSecurityReleases
Microsoft Affected
Microsoft Office 2013 Service Pack 1
Before 5381.1000
Microsoft Affected
Microsoft Office 2016
Before 5215.1000
Microsoft Affected
Microsoft Office 2019
Before https://aka.ms/OfficeSecurityReleases
View vendor advisory (opens in new tab)
Published
15 Sep 2021
Exploitation Attempts Reported
28 Mar 2022
Attack vector
Local
Complexity
Low
Privileges
None
User interaction
Required

Tags

ransomware microsoft cisa malware

CVE References

Exploitation evidence

Evidence of exploitation attempts

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploitation Attempts Observed in the Wild

CISA

Recorded 28 Mar 2022

A trusted third party reported exploitation attempts.

Targeted by Malware-Related Exploitation Attempts

CISA

Recorded 28 Mar 2022

Exploitation attempts against this vulnerability are associated with malware-related payloads.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
CISA First 2022-03-28 00:00 UTC
CVE 2026-08-10 15:31 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

No detection artifacts or sensor request patterns are available for this CVE yet.

Check back as sensor telemetry and scanner integrations are updated.

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

7.8 High

Potential damage if exploited. Separate from whether attackers are using it.

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS

8.0%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

All CVSS Scores

CVSS v3.1 7.8 High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS v2.0 6.8 Medium

AV:N/AC:M/Au:N/C:P/I:P/A:P

Timeline

From disclosure to observed exploitation attempts

  1. 15:31 UTC

    KEV confirmed by CVE

    Exploitation attempts reported by an external source

  2. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  3. 00:00 UTC

    Targeted by malware-related exploitation attempts

    Malware-related exploitation attempts or payloads reported

  4. 11:24 UTC

    CVE published

    Vulnerability disclosed publicly

  5. 00:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2021-38646

Sample API response 
{
  "cve_id": "CVE-2021-38646",
  "confidence": "Confirmed",
  "cvss_score": 7.8,
  "cvss_estimated": false,
  "epss_score": 0.07987,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}