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This advisory has been withdrawn (2021-10-06).
Categories
CVE-2021-31957 medium CVSS 5.9

Vulnerability in ASP.NET Core (CVE-2021-31957)

Summary

Vulnerability in ASP.NET Core (CVE-2021-31957). Risk of unauthorized operations or information disclosure.

Original description

The description as published by the source.

Withdrawn

This advisory was initially published and mapped incorrectly to nuget Microsoft.NETCore.App.Ref. We later reanalyzed this advisory and found it does not have a direct mapping to a NuGet package. Thus we have withdrawn this advisory.

The underlying ASP.NET Core Denial of Service Vulnerability and CVE-2021-31957 remain legitimate.

Description.

Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 5.0 and .NET Core 3.1. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

A denial of service vulnerability exists when ASP.NET Core improperly handles client disconnect. An attacker who successfully exploited this vulnerability could cause a denial of service against an ASP.NET Core web application. The vulnerability can be exploited remotely, without authentication.

Patches

Other Details

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A weakness called CVE-2021-31957 was discovered in ASP.NET Core.
Severity is Medium (CVSS 5.9/10). Exploitation requires specific conditions but can cause real harm if successful.
What you should do: update the affected software to the latest version. If unsure, ask your IT team or search the vendor's site for "ASP.NET Core CVE-2021-31957".

CVE-2021-31957 (ASP.NET Core). Severity: Medium / CVSSv3 5.9. Category: CWE-400.
Response plan:

  1. Check the vendor advisory for affected versions and the patched release.
  2. If a vulnerable version is running in production, schedule maintenance (urgency from KEV/CVSS).
  3. If no patch yet, mitigate via WAF rule, disabling the affected feature, etc.
  4. Monitor logs / SIEM for known IOC and PoC signatures of this CVE.
    PoCs and fix commits: see the 'References' section, MITRE, and NVD.
❓ What is the problem

A weakness (CVE-2021-31957) in ASP.NET Core. A serious software flaw has been identified.

📍 Affected scope

Target versions of ASP.NET Core (see vendor advisory). If running in production, identify exposure immediately.

🔥 Severity

Severity: Medium (CVSS 5.9/10). Exploitation requires specific conditions but can cause real harm if successful.

🔧 How to fix

Update to the patched release as listed in the vendor advisory. (Typical mitigation pattern for CWE-400)

🛡️ Workaround

If a patch is not yet available, consider disabling the affected feature, applying WAF rules, blocking via network ACLs, or isolating the vulnerable version.

🔍 Detection

Check version information, scan dependencies via SBOM, and monitor SIEM for IOC and PoC signatures related to this CVE.

Affected packages

Bitnami dotnet-sdk
[{"type":"SEMVER","events":[{"introduced":"5.0.0"},{"fixed":"5.0.7"}]}]
Bitnami dotnet
[{"type":"SEMVER","events":[{"introduced":"5.0.0"},{"fixed":"5.0.7"}]}]
NuGet Microsoft.NETCore.App.Ref
[{"type":"ECOSYSTEM","events":[{"introduced":"5.0.0"},{"fixed":"5.0.7"}]}]

References

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