CVE-2021-40444
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Microsoft MSHTML Remote Code Execution Vulnerability
rank 72 = 40 + 17 + 0 + 9 + 6
rank@v1 · act now
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.97450 · CISA KEV listed · without this subject the record ranks 32
What it costs you if it fires
NVD CVSS base score, then the CNA's own
CVSS 6.8, from NVD · without this subject the record ranks 55
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
no persisting rise in 365 days · without this subject the record ranks 72
How much of the world it touches
NVD CPE configurations
13 products in the CPE ranges · without this subject the record ranks 63
Someone else already set the date
CISA KEV remediation due date
CISA remediation date held · without this subject the record ranks 66
$3.89M = $4.99M incident cost x 0.8004932139359172 exposure x 0.9745 likelihood
udv@v1 · unaudited · wrong for you until you say what you run
$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.
Hindsight · the state
Foresight · where to check next
This record is one instance of CWE-22, improper limitation of a pathname to a restricted directory ('path traversal'). The index holds 10300 prior instances of this class, 93 KEV-listed. The nearest of its KEV-listed records are drawn beside this. taxonomy@v1
Sources disagree here.
Both shown, dated. We don't pick winners. disagreement-rules@v1
Running Microsoft Windows 10 Version 1507? Check your version
A deterministic range check against the ranges this record publishes. It tells you where a version sits in the record, not whether your deployment is exploitable. No account needed.
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Harm, if it fires from the vector and the weakness
Written for the ticket you're about to file.
CISA KEV & Federal Remediation Deadline from the record and CISA
The fix, and how long it's been waiting.
Exploit Status & Known PoCs a ladder, not a score
Current rung: Ransomware campaign use known, 2021-11-03.
Affected & Fixed Versions as published
Show all 13 published ranges
A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.
What it is stated by the CNA
Microsoft is investigating reports of a remote code execution vulnerability in MSHTML that affects Microsoft Windows. Microsoft is aware of targeted attacks that attempt to exploit this vulnerability by using specially-crafted Microsoft Office documents. An attacker could craft a malicious ActiveX control to be used by a Microsoft Office document that hosts the browser rendering engine. The attacker would then have to convince the user to open the malicious document. receipt
Read the rest of the CNA's description
Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights. Microsoft Defender Antivirus and Microsoft Defender for Endpoint both provide detection and protections for the known vulnerability. Customers should keep antimalware products up to date. Customers who utilize automatic updates do not need to take additional action. Enterprise customers who manage updates should select the detection build 1.349.22.0 or newer and deploy it across their environments. Microsoft Defender for Endpoint alerts will be displayed as: “Suspicious Cpl File Execution”. Upon completion of this investigation, Microsoft will take the appropriate action to help protect our customers. This may include providing a security update through our monthly release process or providing an out-of-cycle security update, depending on customer needs. Please see the Mitigations and Workaround sections for important information about steps you can take to protect your system from this vulnerability. UPDATE September 14, 2021: Microsoft has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. Please see the FAQ for important information about which updates are applicable to your system.
NVD's analysis a second authority
- severity
- 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P
- weakness
- CWE-22
- affected versions
- microsoft windows 10 1507 < 10.0.10240.19060; microsoft windows 10 1607 < 10.0.14393.4651; microsoft windows 10 1809 < 10.0.17763.2183; and 10 more, listed in full below
- also scored by
- [email protected] 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L · [email protected] 7.8 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
The CNA scored it 8.8 and NVD 6.8. Both are shown because both were published; we do not pick one.
check it yourself msrc.microsoft.com receipt
Dated events
Movement the material steps
Show all 64 observations
64 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt
The full biography
Listed by CISA 49 days after it published and the record had been public for 4 years, 11 months when this index was last written.
No material movement in 24 days as of the last ingest this index recorded.
The pattern, elsewhere
This record is one instance of CWE-22, improper limitation of a pathname to a restricted directory ('path traversal'). The index holds 10300 prior instances of this class, 93 KEV-listed. The nearest of its KEV-listed records are drawn beside this. [email protected]
"Matches n of m" counts the attributes the two records can both be compared on: the CVSS metrics they share a version of, any weakness class beyond this one, and the vendor. fit-rules@v1
10300 records in this class held. The six above are drawn from the ones CISA has listed as exploited, ranked by how much of the record matches this one. That is why every one of them is KEV-listed: the pool is, so the colour on those spokes says nothing the pool has not already said.
No curated product neighbourhood is held for this product, so the records above are the nearest this index can name. The neighbourhood table covers a small set of products and is extended by hand.
Siblings and hubs
Records related to this one
No record cites this identifier and it carries no alias. Its defect family is below.
Its defect family
microsoft windows 10 version 1507
Of the 3 records in this family, this is the only one holding a stated fix version: 10.0.10240.19060; 10.0.14393.4651; 10.0.17763.2183; 10.0.183.
Grouped by shared product and weakness, not by shared vulnerability. Each record's own state is on its own page.
Family membership: held values
This record is one of a group, and the group's page describes all of them. This page is kept and dated, and the defect family's own page is the one we offer for indexing: the whole group.
Browse the index from here
These are index-wide views, not findings about CVE-2021-40444.
What usually comes next
Everything above needs no account. What is below is work: assembling it, scoping it to your estate, watching it, and handing it to someone else.