Skip to content
Fencer Vulns
high 7.5

CVE-2020-1045 json

Microsoft ASP.NET Core Security Feature Bypass Vulnerability

published 2020-09-11 6 y ago modified 2026-09-08 2 mo ago also BIT-aspnet-core-2020-1045 , EUVD-2022-4249 , GHSA-hxrm-9w7p-39cc

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
5.9%
EPSS 5.9% chance of exploitation in 30 days, percentile 93%
public exploits
0
none known

Summary

<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>

Patch / fix

  • nuget Microsoft.AspNetCore.Http 2.1.22
  • nuget Microsoft.AspNetCore.App 2.1.22
  • nuget Microsoft.Owin 4.1.1
  • nuget Microsoft.AspNetCore.App.Runtime.linux-arm 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.linux-arm64 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.linux-musl-x64 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.linux-x64 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.osx-x64 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.win-arm 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.win-x64 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.win-x86 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 3.1.8
  • nuget Microsoft.AspNetCore.App.Runtime.win-arm64 3.1.8
  • bitnami aspnet-core 3.1.8
  • microsoft asp.net_core 3.1.8
  • rh-dotnet31-dotnet RHEL 3.1 DOTNET 3.1.108-1.el7
  • rh-dotnet31-dotnet-host RHEL 3.1 DOTNET 3.1.8-1.el7
  • rh-dotnet31-dotnet-sdk-3.1 RHEL 3.1 DOTNET 3.1.108-1.el7
  • rh-dotnet31-dotnet-hostfxr-3.1 RHEL 3.1 DOTNET 3.1.8-1.el7
  • rh-dotnet31-dotnet-runtime-3.1 RHEL 3.1 DOTNET 3.1.8-1.el7
  • rh-dotnet31-dotnet-templates-3.1 RHEL 3.1 DOTNET 3.1.108-1.el7
  • rh-dotnet31-aspnetcore-runtime-3.1 RHEL 3.1 DOTNET 3.1.8-1.el7
  • rh-dotnet31-dotnet-apphost-pack-3.1 RHEL 3.1 DOTNET 3.1.8-1.el7

red hat advisories RHSA-2020:3697RHSA-2020:3699

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-1045 updated cvss 7.5

dotnet: ASP.NET cookie prefix spoofing vulnerability

  • Red Hat .NET Core on Red Hat Enterprise Linux ComputeNode (v. 7) rh-dotnet31-dotnet 3.1.108-1.el7, rh-dotnet31-dotnet-host 3.1.8-1.el7, rh-dotnet31-dotnet-sdk-3.1 3.1.108-1.el7, rh-dotnet31-dotnet-hostfxr-3.1 3.1.8-1.el7, rh-dotnet31-dotnet-runtime-3.1 3.1.8-1.el7, rh-dotnet31-aspnetcore-runtime-3.1 3.1.8-1.el7, +5 more Red Hat .NET Core on Red Hat Enterprise Linux Server (v. 7) rh-dotnet31-dotnet 3.1.108-1.el7, rh-dotnet31-dotnet-host 3.1.8-1.el7, rh-dotnet31-dotnet-sdk-3.1 3.1.108-1.el7, rh-dotnet31-dotnet-hostfxr-3.1 3.1.8-1.el7, rh-dotnet31-dotnet-runtime-3.1 3.1.8-1.el7, rh-dotnet31-aspnetcore-runtime-3.1 3.1.8-1.el7, +5 more Red Hat .NET Core on Red Hat Enterprise Linux Workstation (v. 7) rh-dotnet31-dotnet 3.1.108-1.el7, rh-dotnet31-dotnet-host 3.1.8-1.el7, rh-dotnet31-dotnet-sdk-3.1 3.1.108-1.el7, rh-dotnet31-dotnet-hostfxr-3.1 3.1.8-1.el7, rh-dotnet31-dotnet-runtime-3.1 3.1.8-1.el7, rh-dotnet31-aspnetcore-runtime-3.1 3.1.8-1.el7, +5 more
    fixed: vendor fix RHSA-2020:3697
  • Red Hat Enterprise Linux AppStream (v. 8) dotnet 3.1.108-2.el8_2, dotnet-host 3.1.8-2.el8_2, dotnet3.1 3.1.108-2.el8_2, dotnet-sdk-3.1 3.1.108-2.el8_2, dotnet-hostfxr-3.1 3.1.8-2.el8_2, dotnet-runtime-3.1 3.1.8-2.el8_2, +6 more
    fixed: vendor fix RHSA-2020:3699
  • Red Hat .NET Core 2.1 on Red Hat Enterprise Linux rh-dotnet21, rh-dotnet21-runtime Red Hat Enterprise Linux 8 dotnet, dotnet-host, dotnet-sdk-2.1, dotnet-runtime-2.1, dotnet-sdk-2.1.5xx, dotnet-host-fxr-2.1
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2 y ago

Exploit prediction

5.93% chance of exploitation in the next 30 days, higher than 93% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 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
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:P/A:N
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
nuget Microsoft.AspNetCore.Http
<2.1.22
2.1.22
nuget Microsoft.AspNetCore.App
<2.1.22
2.1.22
nuget Microsoft.Owin
<4.1.1
4.1.1
nuget Microsoft.AspNetCore.App.Runtime.linux-arm
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.linux-arm64
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.linux-musl-x64
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.linux-x64
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.osx-x64
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.win-arm
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.win-x64
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.win-x86
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.linux-musl-arm64
>=3.1.0, <3.1.8
3.1.8
nuget Microsoft.AspNetCore.App.Runtime.win-arm64
>=3.1.5, <3.1.8
3.1.8
bitnami aspnet-core
>=3.1.0, <3.1.8
3.1.8

Affected products

  • Microsoft ASP.NET Core 2.1
  • Microsoft ASP.NET Core 3.1

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.