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NVD / CVE Program· CNA microsoft

CVE-2021-33742: Windows MSHTML Platform Remote Code Execution Vulnerability

Noroxi assessment

Priority: This week (action score 78/100)

  • CISA has confirmed exploitation in the wild (Nov 3, 2021). Remediation deadline for US federal agencies: Nov 17, 2021.
  • Probability of exploitation in the next 30 days: 59.4% (FIRST EPSS); higher than 99.1% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. Special conditions such as timing or configuration are required.
  • According to the record, no fixed version is available yet.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Don’t wait for the next maintenance window. Until a fix is released, restrict access to the affected component and follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · CISA KEV · FIRST EPSS

HighCVSS 7.5 · v3.1KEVWeaponized No fix recorded
Published
Jun 8, 2021
Updated
Jun 16, 2026
EPSS
59.4% · 99th percentile

Report tools

JSON

Action score

78

This week

Don’t wait for the next maintenance window.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
30 / 30 · Listed
EPSS
18 / 30 · 59.4%

CISA SSVC decision

Exploitation
active
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · microsoft
7.5
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Nov 3, 2021. That signals real attacks, not theory.

Remediation deadline for US federal agencies: Nov 17, 2021.

Get told when this record changes

  • In CISA KEV: exploitation in the wild confirmed
  • Weaponized exploit exists
  • No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-33742

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
microsoftwindows 10 1507
microsoftwindows 10 1607
microsoftwindows 10 1809
microsoftwindows 10 1909
microsoftwindows 10 2004
microsoftwindows 10 20h2
microsoftwindows 10 21h1
microsoftwindows 7
microsoftwindows 8.1
microsoftwindows rt 8.1
microsoftwindows server 2008
microsoftwindows server 2012

and 2 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • microsoft windows server 2008r2
  • microsoft windows server 2008sp2
  • microsoft windows server 2012all versions
  • microsoft windows server 2012r2
  • microsoft windows server 2016before 10.0.14393.4467
  • microsoft windows server 2019before 10.0.17763.1999

Versions reported by the vendor

Affected version ranges reported by the assigning authority (microsoft). Independent of NVD's CPE analysis and usually ahead of it.

  • Microsoft Windows 10 Version 1507

    • 10.0.0 and later · before 10.0.10240.18967affected

  • Microsoft Windows 10 Version 1607

    • 10.0.0 and later · before 10.0.14393.4467affected

  • Microsoft Windows 10 Version 1809

    • 10.0.0 and later · before 10.0.17763.1999affected

  • Microsoft Windows 10 Version 1909

    • 10.0.0 and later · before 10.0.18363.1621affected

  • Microsoft Windows 10 Version 2004

    • 10.0.0 and later · before 10.0.19041.1052affected

  • Microsoft Windows 10 Version 20H2

    • 10.0.0 and later · before 10.0.19042.1052affected

  • Microsoft Windows 10 Version 21H1

    • 10.0.0 and later · before 10.0.19043.1052affected

  • Microsoft Windows 7

    • 6.1.0 and later · before 6.1.7601.25632affected
    • 6.1.0 and later · before publicationaffected

  • Microsoft Windows 7 Service Pack 1

    • 6.1.0 and later · before 6.1.7601.25632affected
    • 6.1.0 and later · before publicationaffected

  • Microsoft Windows 8.1

    • 6.3.0 and later · before 6.3.9600.20045affected
    • 6.3.0 and later · before 1.0.0.0affected

  • Microsoft Windows Server 2008 Service Pack 2

    • 6.0.0 and later · before 6.0.6003.21137affected
    • 6.0.0 and later · before publicationaffected

  • Microsoft Windows Server 2008 R2 Service Pack 1

    • 6.1.0 and later · before 6.1.7601.25632affected
    • 6.1.0 and later · before publicationaffected

Same product

microsoft: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-34527Windows Print Spooler Remote Code Execution VulnerabilityKEV
    95Now
  • CVE-2021-40444Microsoft MSHTML Remote Code Execution VulnerabilityKEV
    94Now
  • CVE-2025-33053Internet Shortcut Files Remote Code Execution VulnerabilityKEV
    91Now

Published before and after this one in the same product

  • ← EarlierCVE-2021-31201Jun 8, 2021 · Microsoft Enhanced Cryptographic Provider Elevation of Privilege VulnerabilityKEV
    51Plan
  • ← EarlierCVE-2021-31956Jun 8, 2021 · Windows NTFS Elevation of Privilege VulnerabilityKEV
    68This week
  • Later →CVE-2021-31979Jul 14, 2021 · Windows Kernel Elevation of Privilege VulnerabilityKEV
    62This week

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. CISA KEV+147 d
  3. TodayNov 6, 2026+1977 d

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • A user must open a link or visit a page.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-787 · Out-of-bounds Write

CVSS vector

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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records