CVE-2021-31955 [Exploited] | Microsoft WINDOWS 10 1809 Information Disclosure

CVE-2021-31955 is rated Active Exploitation (77.3/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 3.61%). CISA KEV confirms active exploitation (added 2021-11-03) affecting Microsoft / Windows. a weakness (CWE-497) Unauthenticated remote administrative access may be possible. The CISA remediation deadline has passed—treat as an emergency patch priority.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-22	4.07%	3.61%	-0.46%
2	2026-05-02	4.32%	4.07%	-0.25%
3	2026-04-29	—	4.32%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-22

4.07%

3.61%

-0.46%

2026-05-02

4.32%

4.07%

-0.25%

2026-04-29

—

4.32%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
5.5	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. 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:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. 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:N) Data isn’t meaningfully altered or forged. Availability (A:N) Service keeps running; no real outage angle.	1.8	3.6	[email protected]
5.5	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. 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:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. 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:N) Data isn’t meaningfully altered or forged. Availability (A:N) Service keeps running; no real outage angle.	1.8	3.6	[email protected]
2.1	2.0	LOW	`AV:L/AC:L/Au:N/C:P/I:N/A:N` Click to expand Access vector (AV:L) Requires local access to the target system. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:N) No availability impact.	3.9	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

5.5

3.1

MEDIUM

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

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
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:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
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:N): Data isn’t meaningfully altered or forged.
Availability (A:N): Service keeps running; no real outage angle.

1.8

3.6

[email protected]

5.5

3.1

MEDIUM

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

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
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:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
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:N): Data isn’t meaningfully altered or forged.
Availability (A:N): Service keeps running; no real outage angle.

1.8

3.6

[email protected]

2.1

2.0

LOW

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

Access vector (AV:L): Requires local access to the target system.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:N): No availability impact.

3.9

2.9

[email protected]

Affected software / configurations for CVE-2021-31955

Vendor	Product	Version	Raw CPE
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_server_2004	< 10.0.19041.1052	cpe:2.3:o:microsoft:windows_server_2004::::::::
microsoft	windows_server_2019	< 10.0.17763.1999	cpe:2.3:o:microsoft:windows_server_2019::::::::
microsoft	windows_server_20h2	< 10.0.19042.1052	cpe:2.3:o:microsoft:windows_server_20h2::::::::

References for CVE-2021-31955

URL	Tags
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31955	Patch Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31955	US Government Resource

URL

CVE-2021-31955 | Windows Kernel Information Disclosure Vulnerability

CISA KEV Record for CVE-2021-31955

Exploit prediction scoring system (EPSS) score for CVE-2021-31955

Common vulnerability scoring system (CVSS) metrics for CVE-2021-31955

Weakness enumeration for CVE-2021-31955

Affected software / configurations for CVE-2021-31955

References for CVE-2021-31955