CVE-2021-38646
CVE-2021-38646 is a security flaw in Microsoft Office, part of Microsoft Office. Attackers can run their own code on Microsoft Office. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 28 Mar 2022, and says ransomware gangs have used it.[1]
Microsoft Office is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Fixed in version https://aka.ms/OfficeSecurityReleases, 5381.1000 and 5215.1000.
Description
CISA calls it an access connectivity engine remote code execution in Microsoft Office. In its words: “Microsoft Office Access Connectivity Engine contains an unspecified vulnerability which can allow for remote code execution.”[1]
It scores 7.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| Microsoft 365 Apps for Enterprise | https://aka.ms/OfficeSecurityReleases |
| Microsoft Office 2013 Service Pack 1 | 5381.1000 |
| Microsoft Office 2016 | 5215.1000 |
| Microsoft Office 2019 | https://aka.ms/OfficeSecurityReleases |
Every device with Microsoft Office needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 28 Mar 2022, 194 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 18 Apr 2022 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 8%. That’s in the top 6% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Microsoft has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update Microsoft Office now.On Windows: Settings, Windows Update, Check for updates, then restart. Office updates come the same way, or from any Office app: File, Account, Update Options. Then turn on automatic updates, so the next fix arrives on its own.
- Check you’re on https://aka.ms/OfficeSecurityReleases or later.Fixed in version https://aka.ms/OfficeSecurityReleases, 5381.1000 and 5215.1000. Anything older is what attackers are going after.
- If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 8%.[4] |
See also
Other Microsoft Office flaws
- CVE-2009-0238: remote code execution ·
- CVE-2026-21514: word reliance on untrusted inputs in a security decision ·
- CVE-2026-21509: security feature bypass ·
- CVE-2009-0556: powerPoint code injection ·
- CVE-2007-0671: excel remote code execution ·
- CVE-2023-23397: outlook privilege escalation ·
Other Microsoft flaws
- CVE-2026-96951, Microsoft Windows: command injection ·
- CVE-2026-65660, Microsoft SharePoint: code injection ·
- CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
- CVE-2026-81963, Microsoft Windows: link following ·
- CVE-2019-1068, Microsoft SQL Server: remote code execution ·
Similar flaws
- CVE-2026-111357, Ivanti Connect Secure: missing authentication for critical function ·
- CVE-2026-97229, GitLab Community Edition and Enterprise Edition: integer overflow or wraparound ·
- CVE-2026-76418, Cisco Secure Firewall ASA Software and Cisco Secure FTD Software: unchecked return value to NULL pointer dereference ·
- CVE-2026-48356, Adobe Commerce and Magento: unrestricted upload of file with dangerous type ·
- CVE-2026-111497, Google Brotli: unchecked return value ·
Added the same day
- CVE-2022-1096, Chrome and other Chromium browsers: type confusion ·
- CVE-2022-0543, Redis Debian-specific Redis Servers: debian-specific redis server lua sandbox escape ·
- CVE-2021-34486, Microsoft Windows: event tracing privilege escalation ·
- CVE-2021-26085, Atlassian Confluence Server: pre-authorization arbitrary file read ·
- CVE-2021-20028, SonicWall Secure Remote Access (SRA): SQL injection ·
Every Microsoft flaw on CISA’s list · Everything added in March 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability”. Known Exploited Vulnerabilities Catalog, added 28 Mar 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-38646 Detail”. National Vulnerability Database, published 15 Sep 2021.
- ^ Microsoft. Advisories and fixes: msrc.microsoft.com, portal.msrc.microsoft.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.080, percentile 94.8, 31 Oct 2026.
- CVE Program. “CVE-2021-38646”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.