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CVE-2020-1045

Microsoft ASP.NET Core Security Feature Bypass Vulnerability

7.5 HighFix available

<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>

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
High
Availability
None

Exploit likelihood

5.93%Down 2.8 points since Apr 14, 2021
90%50%10%1%

What each source reports

CVE List Score used 7.5

Microsoft ASP.NET Core Security Feature Bypass Vulnerability

<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>

Record
CVE-2020-1045
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C
Updated
2026-11-02
EUVDEUVD-2022-4249 7.5

<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>

Record
EUVD-2022-4249
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C
Updated
2026-11-03
GitHub AdvisoriesGHSA-hxrm-9w7p-39cc 7.5

Cookie parsing failure

A security feature bypass vulnerability exists in the way Microsoft ASP.NET Core parses encoded cookie names.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.The security update addresses the vulnerability by fixing the way the ASP.NET Core cookie parser handles encoded names., aka 'Microsoft ASP.NET Core Security Feature Bypass Vulnerability'.

Record
GHSA-hxrm-9w7p-39cc
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
NVD 7.5

<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>

Record
CVE-2020-1045
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:P/A:N
Updated
2026-11-02
OSV 7.5

<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>

Record
CVE-2020-1045
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVGHSA-hxrm-9w7p-39cc 7.5

Cookie parsing failure

A security feature bypass vulnerability exists in the way Microsoft ASP.NET Core parses encoded cookie names.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.The security update addresses the vulnerability by fixing the way the ASP.NET Core cookie parser handles encoded names., aka 'Microsoft ASP.NET Core Security Feature Bypass Vulnerability'.

Record
GHSA-hxrm-9w7p-39cc
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVRHSA-2020:3697 7.5

Red Hat Security Advisory: .NET Core 3.1 security and bugfix update for Red Hat Enterprise Linux

Record
RHSA-2020:3697
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVRHSA-2020:3699 7.5

Red Hat Security Advisory: .NET Core 3.1 security and bugfix update

Record
RHSA-2020:3699
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVBIT-aspnet-core-2020-1045 No score

Microsoft ASP.NET Core Security Feature Bypass Vulnerability

<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>

Record
BIT-aspnet-core-2020-1045
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
Microsoft.AspNetCore.App
NuGet
 through 2.1.21
2.1.22
Microsoft.Owin
NuGet
 before 4.1.1
4.1.1
Microsoft.AspNetCore.App.Runtime.linux-arm
NuGet
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.App.Runtime.linux-arm64
NuGet
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.App.Runtime.linux-musl-arm64
NuGet
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.App.Runtime.linux-musl-x64
NuGet
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.App.Runtime.linux-x64
NuGet
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.App.Runtime.osx-x64
NuGet
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.App.Runtime.win-arm
NuGet
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.App.Runtime.win-x64
NuGet
 3.1.0 up to 3.1.8
3.1.8
Show 48 moreShow less
Affected packages
PackageAffectedFixed
Microsoft.AspNetCore.App.Runtime.win-x86
NuGet
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.App.Runtime.win-arm64
NuGet
 3.1.5 up to 3.1.8
3.1.8
Microsoft.AspNetCore.Http
NuGet
 before 2.1.22
2.1.22
aspnet-core
Bitnami
 3.1.0 up to 3.1.8
3.1.8
Microsoft.AspNetCore.Http
NuGet
 before 2.1.22, plus listed versions
0.0.1-alpha1.0.01.0.0-rc2-final1.0.11.0.2
Show 17 moreShow less
1.0.31.0.41.1.01.1.0-preview1-final1.1.11.1.22.0.02.0.0-preview1-final2.0.0-preview2-final2.0.12.0.22.0.32.1.02.1.0-preview1-final2.1.0-preview2-final2.1.0-rc1-final2.1.1
2.1.22
Microsoft.AspNetCore.App
NuGet
 before 2.1.22, plus listed versions
2.1.02.1.0-preview1-final2.1.0-preview2-final2.1.0-rc1-final2.1.1
Show 20 moreShow less
2.1.102.1.112.1.122.1.132.1.142.1.152.1.162.1.172.1.182.1.192.1.22.1.202.1.212.1.32.1.42.1.52.1.62.1.72.1.82.1.9
2.1.22
Microsoft.Owin
NuGet
 before 4.1.1, plus listed versions
1.1.0-beta11.1.0-beta22.0.02.0.0-rc12.0.1
Show 16 moreShow less
2.0.22.1.02.1.0-rc13.0.03.0.0-alpha13.0.0-beta13.0.0-rc13.0.0-rc23.0.13.1.03.1.0-rc14.0.04.0.0-alpha14.0.0-preview14.0.14.1.0
4.1.1
Microsoft.AspNetCore.App.Runtime.linux-arm
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.linux-arm64
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.linux-musl-x64
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.linux-x64
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.osx-x64
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.win-arm
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.win-x64
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.win-x86
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.linux-musl-arm64
NuGet
 3.1.0 up to 3.1.8, plus listed versions
3.1.13.1.23.1.33.1.43.1.53.1.63.1.7
3.1.8
Microsoft.AspNetCore.App.Runtime.win-arm64
NuGet
 3.1.5 up to 3.1.8, plus listed versions
3.1.63.1.7
3.1.8
rh-dotnet31-aspnetcore-runtime-3.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.8-1.el7
0:3.1.8-1.el7
rh-dotnet31-aspnetcore-targeting-pack-3.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.8-1.el7
0:3.1.8-1.el7
rh-dotnet31-dotnet
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.108-1.el7
0:3.1.108-1.el7
rh-dotnet31-dotnet-apphost-pack-3.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.8-1.el7
0:3.1.8-1.el7
rh-dotnet31-dotnet-debuginfo
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.108-1.el7
0:3.1.108-1.el7
rh-dotnet31-dotnet-host
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.8-1.el7
0:3.1.8-1.el7
rh-dotnet31-dotnet-hostfxr-3.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.8-1.el7
0:3.1.8-1.el7
rh-dotnet31-dotnet-runtime-3.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.8-1.el7
0:3.1.8-1.el7
rh-dotnet31-dotnet-sdk-3.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.108-1.el7
0:3.1.108-1.el7
rh-dotnet31-dotnet-targeting-pack-3.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.8-1.el7
0:3.1.8-1.el7
rh-dotnet31-dotnet-templates-3.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.108-1.el7
0:3.1.108-1.el7
rh-dotnet31-netstandard-targeting-pack-2.1
Red Hat:rhel_dotnet:3.1::el7
 before 0:3.1.108-1.el7
0:3.1.108-1.el7
aspnetcore-runtime-3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
aspnetcore-targeting-pack-3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.108-2.el8_2
0:3.1.108-2.el8_2
dotnet-apphost-pack-3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-apphost-pack-3.1-debuginfo
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-host
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-host-debuginfo
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-hostfxr-3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-hostfxr-3.1-debuginfo
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-runtime-3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-runtime-3.1-debuginfo
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-sdk-3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.108-2.el8_2
0:3.1.108-2.el8_2
dotnet-sdk-3.1-debuginfo
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.108-2.el8_2
0:3.1.108-2.el8_2
dotnet-targeting-pack-3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.8-2.el8_2
0:3.1.8-2.el8_2
dotnet-templates-3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.108-2.el8_2
0:3.1.108-2.el8_2
dotnet3.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.108-2.el8_2
0:3.1.108-2.el8_2
dotnet3.1-debuginfo
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.108-2.el8_2
0:3.1.108-2.el8_2
dotnet3.1-debugsource
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.108-2.el8_2
0:3.1.108-2.el8_2
netstandard-targeting-pack-2.1
Red Hat:enterprise_linux:8::appstream
 before 0:3.1.108-2.el8_2
0:3.1.108-2.el8_2

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2020-1045 is a high vulnerability (CVSS 7.5) in Microsoft Asp.net Core, published September 11, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 5.93%, the 93rd percentile. Fixed in Microsoft.AspNetCore.App 2.1.22.

References

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