CVE-2021-38646 — Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

• Documented patch — msrc.microsoft.com (NIST National Vulnerability Database)
• Documented patch — portal.msrc.microsoft.com (NIST National Vulnerability Database)

CISA required action CISA

Apply updates per vendor instructions.

US federal deadline: Apr 18, 2022 — passed 1641 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

1. Identify exposed assets running the affected vendor/product/version combinations (Microsoft 365 Apps, Microsoft Microsoft 365 Apps for Enterprise, Microsoft Microsoft Office 2013 Service Pack 1…).
2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
3. Apply the fixed version or the patch documented under Remediation.
4. Exploitation requires user interaction: tighten email/web filtering and warn affected users.
5. EPSS ahead of 95% of scored CVEs: prioritize it in the patch queue.
6. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 7.99%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

• Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
• Hunt retroactively in logs from before Mar 28, 2022 (KEV listing): exploitation may have started earlier.

Timeline

What happened to this CVE, newest first.

• 2026
• Affected products added · microsoft/microsoft 365 apps for enterprise, microsoft/microsoft office 2013 service pack 1, microsoft/microsoft office
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• SSVC assessment updated
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• Record published
  Oct 13, 2026
• Fix documented
  Oct 13, 2026 · NIST National Vulnerability Database
• Affected products added · microsoft/365 apps, microsoft/office, microsoft/office 2016, microsoft/office 2019
  Oct 13, 2026 · NIST National Vulnerability Database
• CVSS changed · 7.8
  Oct 13, 2026 · NIST National Vulnerability Database
• Source status changed · → Analyzed
  Oct 13, 2026 · NIST National Vulnerability Database
• Added to CISA KEV (detected)
  Oct 13, 2026 · CISA Known Exploited Vulnerabilities
• Record created in this database
  Oct 13, 2026 · CISA Known Exploited Vulnerabilities
• 2022
• Added to CISA KEV catalog
  Mar 27, 2022 · CISA
• 2021
• CVE published
  Sep 15, 2021 · microsoft

Source activity

Repeated readings are counted rather than listed.

• 2× References added · Oct 13, 2026 – Oct 13, 2026
• 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

5 on the record

• portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-38646
  Patch, Vendor Advisory, NIST National Vulnerability Database
• msrc.microsoft.com/update-guide/vulnerability/CVE-2021-38646
  Patch, Vendor Advisory, vendor-advisory, patch, NIST National Vulnerability Database
• www.cisa.gov/known-exploited-vulnerabilities-catalog
  US Government Resource, NIST National Vulnerability Database
• nvd.nist.gov/vuln/detail/CVE-2021-38646
  GitHub Security Advisories
• github.com/advisories/GHSA-846x-h43v-68x9
  GitHub Security Advisories

Elsewhere on this site

Related CVEs (same products)

• Medium CVE-2026-108455 Microsoft Office PowerPoint Information Disclosure Vulnerability 4h
• Medium CVE-2026-108453 Microsoft Office PowerPoint Information Disclosure Vulnerability 4h
• Medium CVE-2026-108454 Microsoft Office PowerPoint Information Disclosure Vulnerability 4h
• High CVE-2026-108448 Microsoft Office Outlook Remote Code Execution Vulnerability 4h
• High CVE-2026-108447 Microsoft Office Word Remote Code Execution Vulnerability 4h
• High CVE-2026-108451 Microsoft Office Word Remote Code Execution Vulnerability 4h

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

• No CWE classification.
• No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
• No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
• No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-38646 is "Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability", rated High. It affects 365 Apps (Microsoft); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 7.8 describes technical severity. EPSS 7.99% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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