CVE-2021-33742 [Exploited] | Microsoft WINDOWS 10 1507 Out-of-bounds Write

CVE-2021-33742 is rated Critical Active Threat (90.7/100): CVSS High severity, with high exploitation likelihood (EPSS 72.12%, 99th percentile). CISA KEV confirms active exploitation (added 2021-11-03) affecting Microsoft / Windows. a weakness (CWE-787) Unauthenticated remote administrative access may be possible. EPSS rose +1.11% over the last day, indicating growing attacker interest. The CISA remediation deadline has passed—treat as an emergency patch priority.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-04-30	71.00%	72.12%	+1.11%
2	2026-02-09	72.12%	71.00%	-1.11%
3	2026-01-02	—	72.12%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-04-30

71.00%

72.12%

+1.11%

2026-02-09

72.12%

71.00%

-1.11%

2026-01-02

—

72.12%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.5	3.1	HIGH	`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.6	5.9	[email protected]
8.8	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.8	5.9	[email protected]
6.8	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:M) Exploitation needs some favorable conditions, but not exceptional ones. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	8.6	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.5

3.1

HIGH

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

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R): A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.6

5.9

[email protected]

8.8

3.1

HIGH

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

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R): A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.8

5.9

[email protected]

6.8

2.0

MEDIUM

AV:N/AC:M/Au:N/C:P/I:P/A:P Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:M): Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

8.6

6.4

[email protected]

Affected software / configurations for CVE-2021-33742

Vendor	Product	Version	Raw CPE
microsoft	windows_10_1507	< 10.0.10240.18967	cpe:2.3:o:microsoft:windows_10_1507::::::::
microsoft	windows_10_1607	< 10.0.14393.4467	cpe:2.3:o:microsoft:windows_10_1607::::::::
microsoft	windows_10_1809	< 10.0.17763.1999	cpe:2.3:o:microsoft:windows_10_1809::::::::
microsoft	windows_10_1909	< 10.0.18363.1621	cpe:2.3:o:microsoft:windows_10_1909::::::::
microsoft	windows_10_2004	< 10.0.19041.1052	cpe:2.3:o:microsoft:windows_10_2004::::::::
microsoft	windows_10_20h2	< 10.0.19042.1052	cpe:2.3:o:microsoft:windows_10_20h2::::::::
microsoft	windows_10_21h1	< 10.0.19043.1052	cpe:2.3:o:microsoft:windows_10_21h1::::::::
microsoft	windows_7	—	cpe:2.3:o:microsoft:windows_7:-:sp1::::::
microsoft	windows_8.1	—	cpe:2.3:o:microsoft:windows_8.1:-:::::::*
microsoft	windows_rt_8.1	—	cpe:2.3:o:microsoft:windows_rt_8.1:-:::::::*
microsoft	windows_server_2008	r2	cpe:2.3:o:microsoft:windows_server_2008:r2:sp1:::::x64:*
microsoft	windows_server_2008	sp2	cpe:2.3:o:microsoft:windows_server_2008:sp2:::::::*
microsoft	windows_server_2012	—	cpe:2.3:o:microsoft:windows_server_2012:-:::::::*
microsoft	windows_server_2012	r2	cpe:2.3:o:microsoft:windows_server_2012:r2:::::::*
microsoft	windows_server_2016	< 10.0.14393.4467	cpe:2.3:o:microsoft:windows_server_2016::::::::
microsoft	windows_server_2019	< 10.0.17763.1999	cpe:2.3:o:microsoft:windows_server_2019::::::::

References for CVE-2021-33742

URL	Tags
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33742	Patch Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33742	US Government Resource

URL

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

CISA KEV Record for CVE-2021-33742

Exploit prediction scoring system (EPSS) score for CVE-2021-33742

Common vulnerability scoring system (CVSS) metrics for CVE-2021-33742

Weakness enumeration for CVE-2021-33742

Affected software / configurations for CVE-2021-33742

References for CVE-2021-33742