CVE-2021-36934
CVE-2021-36934 is a security flaw in Microsoft Windows, Microsoft’s operating system for PCs and servers. Attackers can run their own code on Microsoft Windows. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 10 Feb 2022.[1]
Microsoft Windows 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 10.0.17763.2114, 10.0.18363.1734, 10.0.19041.1165 and 10.0.19042.1165 and others.
Description
CISA calls it an SAM local privilege escalation in Microsoft Windows. In its words: “If a Volume Shadow Copy (VSS) shadow copy of the system drive is available, users can read the SAM file which would allow any user to escalate privileges to SYSTEM level.”[1]
The CVE record adds: “An elevation of privilege vulnerability exists because of overly permissive Access Control Lists (ACLs) on multiple system files, including the Security Accounts Manager (SAM) database. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. An attacker must have the ability to execute code on a victim system to exploit this vulnerability. After installing this security update, you must manually delete all shadow copies of system files, including the SAM database, to fully mitigate this vulnerabilty. Simply installing this security update will not fully mitigate this vulnerability. See KB5005357- Delete Volume Shadow Copies.”[2]
The underlying weakness is CWE-1220, in MITRE’s list of common software weaknesses.
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 |
|---|---|
| Windows 10 Version 1809 | 10.0.17763.2114 |
| Windows 10 Version 1909 | 10.0.18363.1734 |
| Windows 10 Version 2004 | 10.0.19041.1165 |
| Windows 10 Version 20H2 | 10.0.19042.1165 |
| Windows 10 Version 21H1 | 10.0.19043.1165 |
Every device with Microsoft Windows needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 10 Feb 2022, 203 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 24 Feb 2022 to fix it.[1]
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 67%. That’s in the top 1% 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 Windows 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 10.0.17763.2114 or later.Fixed in version 10.0.17763.2114, 10.0.18363.1734, 10.0.19041.1165 and 10.0.19042.1165 and others. 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.[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 67%.[4] |
See also
Other Microsoft Windows flaws
- CVE-2026-96951: command injection ·
- CVE-2026-85880: heap-based buffer overflow ·
- CVE-2026-81963: link following ·
- CVE-2008-4250: buffer overflow ·
- CVE-2026-32202: protection mechanism failure ·
- CVE-2025-60710: link following ·
Similar flaws
- CVE-2025-31201, Apple devices: arbitrary read and write ·
Added the same day
- CVE-2020-0796, Microsoft SMBv3: remote code execution ·
- CVE-2018-1000861, Jenkins Stapler Web Framework: stapler web framework deserialization of untrusted data ·
- CVE-2017-9791, Apache Struts 1: improper input validation ·
- CVE-2017-8464, Microsoft Windows: shell (.lnk) remote code execution ·
- CVE-2017-10271, Oracle WebLogic Server: corporation webLogic server remote code execution ·
Every Microsoft flaw on CISA’s list · Everything added in February 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Microsoft Windows SAM Local Privilege Escalation Vulnerability”. Known Exploited Vulnerabilities Catalog, added 10 Feb 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-36934 Detail”. National Vulnerability Database, published 22 Jul 2021.
- ^ Microsoft. Advisories and fixes: msrc.microsoft.com, portal.msrc.microsoft.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.673, percentile 99.3, 31 Oct 2026.
- CVE Program. “CVE-2021-36934”. 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.