NVD / CVE Program· CNA microsoft

CVE-2021-31957: ASP.NET Core Denial of Service Vulnerability

MediumCVSS 5.9 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 25/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 5.1% (FIRST EPSS); higher than 92.5% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
Fixed version: aspnetcore-runtime-3.1 (Red Hat:enterprise_linux:8::appstream) 0:3.1.16-1.el8_4; aspnetcore-runtime-5.0 (Red Hat:enterprise_linux:8::appstream) 0:5.0.7-1.el8_4; aspnetcore-targeting-pack-3.1 (Red Hat:enterprise_linux:8::appstream) 0:3.1.16-1.el8_4.

Low priority for now. Upgrade to aspnetcore-runtime-3.1 (Red Hat:enterprise_linux:8::appstream) 0:3.1.16-1.el8_4; aspnetcore-runtime-5.0 (Red Hat:enterprise_linux:8::appstream) 0:5.0.7-1.el8_4; aspnetcore-targeting-pack-3.1 (Red Hat:enterprise_linux:8::appstream) 0:3.1.16-1.el8_4 or later.

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 · FIRST EPSS

Published: Jun 8, 2021
Updated: Oct 7, 2026
EPSS: 5.1% · 92th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 23 / 40 · 5.9 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 2 / 30 · 5.1%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · microsoft: 5.9; NVD has not scored this yet; the score shown is the CNA’s.

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

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

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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

Is your version affected? Check it

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.

Vendor	Product	CPE
microsoft	.net	cpe:2.3:a:microsoft:.net
microsoft	.net core	cpe:2.3:a:microsoft:.net_core
microsoft	visual studio 2019	cpe:2.3:a:microsoft:visual_studio_2019
fedoraproject	fedora	cpe:2.3:o:fedoraproject:fedora

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 .NET 5.0
- 5.0.0 and later · before 5.0.7affected
Microsoft .NET Core 3.1
- 3.1 and later · before 3.1.16affected
Microsoft Microsoft Visual Studio 2019 version 16.10 (includes 16.0 - 16.9)
- 16.10.0 and later · before 16.10.1affected
Microsoft Microsoft Visual Studio 2019 version 16.4 (includes 16.0 - 16.3)
- 16.0 and later · before 16.4.23affected
Microsoft Microsoft Visual Studio 2019 version 16.7 (includes 16.0 – 16.6)
- 16.0.0 and later · before 16.7.16affected
Microsoft Microsoft Visual Studio 2019 version 16.9 (includes 16.0 - 16.8)
- 15.0.0 and later · before 16.9.7affected
Microsoft Visual Studio 2019 for Mac version 8.10
- 8.1.0 and later · before 8.10.1affected

Affected versions · NVD (6)

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

fedoraproject fedora33
fedoraproject fedora34
microsoft .net5.0 and later · up to 5.0.6 inclusive
microsoft .net core3.1 and later · up to 3.1.15 inclusive
microsoft visual studio 201916.0 and later · up to 16.10 inclusive
microsoft visual studio 20198.10

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Red Hat:enterprise_linux:8::appstream	aspnetcore-runtime-3.1	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4
Red Hat:enterprise_linux:8::appstream	aspnetcore-runtime-5.0	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	aspnetcore-targeting-pack-3.1	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4
Red Hat:enterprise_linux:8::appstream	aspnetcore-targeting-pack-5.0	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet	before 0:5.0.204-1.el8_4	0:5.0.204-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-apphost-pack-3.1	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-apphost-pack-3.1-debuginfo	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-apphost-pack-5.0	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-apphost-pack-5.0-debuginfo	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-host	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-host-debuginfo	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-hostfxr-3.1	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-hostfxr-3.1-debuginfo	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-hostfxr-5.0	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-hostfxr-5.0-debuginfo	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-runtime-3.1	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-runtime-3.1-debuginfo	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-runtime-5.0	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-runtime-5.0-debuginfo	before 0:5.0.7-1.el8_4	0:5.0.7-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-sdk-3.1	before 0:3.1.116-1.el8_4	0:3.1.116-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-sdk-3.1-debuginfo	before 0:3.1.116-1.el8_4	0:3.1.116-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-sdk-5.0	before 0:5.0.204-1.el8_4	0:5.0.204-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-sdk-5.0-debuginfo	before 0:5.0.204-1.el8_4	0:5.0.204-1.el8_4
Red Hat:enterprise_linux:8::appstream	dotnet-targeting-pack-3.1	before 0:3.1.16-1.el8_4	0:3.1.16-1.el8_4

+34

Same product

microsoft: all records

Other highest-scoring records for the same primary product.

CVE-2023-38180.NET and Visual Studio Denial of Service VulnerabilityKEV
64This week
CVE-2023-38171Microsoft QUIC Denial of Service Vulnerability
51Plan
CVE-2021-26701.NET Core Remote Code Execution Vulnerability
41Plan

Published before and after this one in the same product

← EarlierCVE-2021-24112Feb 25, 2021 · .NET Core Remote Code Execution Vulnerability
33Monitor
← EarlierCVE-2021-31204May 11, 2021 · .NET and Visual Studio Elevation of Privilege Vulnerability
29Monitor
Later →CVE-2021-26423Aug 12, 2021 · .NET Core and Visual Studio Denial of Service Vulnerability
31Monitor

Remediation

Which version to upgrade to

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

Product / package	Fixed version	Source
red hat:rh-dotnet31-aspnetcore-runtime-3.1	0:3.1.16-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-aspnetcore-targeting-pack-3.1	0:3.1.16-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet	0:3.1.116-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet-apphost-pack-3.1	0:3.1.16-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet-debuginfo	0:3.1.116-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet-host	0:3.1.16-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet-hostfxr-3.1	0:3.1.16-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet-runtime-3.1	0:3.1.16-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet-sdk-3.1	0:3.1.116-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet-targeting-pack-3.1	0:3.1.16-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-dotnet-templates-3.1	0:3.1.116-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)
red hat:rh-dotnet31-netstandard-targeting-pack-2.1	0:3.1.116-1.el7_9 · Red Hat:rhel_dotnet:3.1::el7	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

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.

No dated events beyond publication.

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
Special conditions such as timing or configuration are required.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

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

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

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

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log (2)

SSVC exploitation— → noneOct 7, 2026, 6:07 PM UTC
Fix✗ → ✓Sep 28, 2026, 10:47 PM UTC

For records you follow, these changes also arrive as notifications. →

References

lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4PRVVLXXQEF4SEJOBV3VRJHGX7YHY2CG/

Show all references (4 more)

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

All records