CVE-2021-1721 [Medium] | Denial of Service in .net

CVE-2021-1721 is rated Moderate Risk (56.5/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 3.34%). Review affected assets and schedule remediation.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-18	3.37%	3.34%	-0.03%
2	2026-06-15	9.34%	3.37%	-5.97%
3	2026-01-16	—	9.34%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-18

3.37%

3.34%

-0.03%

2026-06-15

9.34%

3.37%

-5.97%

2026-01-16

—

9.34%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
6.5	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.8	3.6	[email protected]
6.5	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.8	3.6	[email protected]
4.3	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:N/I:N/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:N) No confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:P) Partial availability impact.	8.6	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

6.5

3.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.8

3.6

[email protected]

6.5

3.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.8

3.6

[email protected]

4.3

2.0

MEDIUM

AV:N/AC:M/Au:N/C:N/I:N/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:N): No confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:P): Partial availability impact.

8.6

2.9

[email protected]

OS Trackers for CVE-2021-1721

vendor	priority	summary	link
`redhat`	high	—	https://access.redhat.com/security/cve/CVE-2021-1721

vendor

priority

summary

link

redhat

high

—

https://access.redhat.com/security/cve/CVE-2021-1721

Affected software / configurations for CVE-2021-1721

Vendor	Product	Version	Raw CPE
microsoft	.net	>= 5.0, <= 5.0.2	cpe:2.3:a:microsoft:.net::::::::
microsoft	.net_core	>= 2.1, <= 2.1.24	cpe:2.3:a:microsoft:.net_core::::::::
microsoft	.net_core	>= 3.1, <= 3.1.11	cpe:2.3:a:microsoft:.net_core::::::::
microsoft	powershell_core	7.0	cpe:2.3:a:microsoft:powershell_core:7.0:::::::*
microsoft	powershell_core	7.1	cpe:2.3:a:microsoft:powershell_core:7.1:::::::*
microsoft	visual_studio_2017	>= 15.0, <= 15.9	cpe:2.3:a:microsoft:visual_studio_2017::::::::
microsoft	visual_studio_2019	>= 16.0, <= 16.8	cpe:2.3:a:microsoft:visual_studio_2019::::::::

References for CVE-2021-1721

URL	Tags
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-1721	Patch Vendor Advisory

URL

CVE-2021-1721 | .NET Core and Visual Studio Denial of Service Vulnerability

Exploit prediction scoring system (EPSS) score for CVE-2021-1721

Common vulnerability scoring system (CVSS) metrics for CVE-2021-1721

Weakness enumeration for CVE-2021-1721

GitHub Security Advisory for CVE-2021-1721

OS Trackers for CVE-2021-1721

Affected software / configurations for CVE-2021-1721

References for CVE-2021-1721