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.NET NuGet

CVE-2020-1045

HIGH

Cookie parsing failure

Also known asBIT-aspnet-core-2020-1045GHSA-hxrm-9w7p-39cc
Published
Sep 11, 2020
Updated
Apr 10, 2026
Affected
13 pkgs
Patched
13 / 13
Exploits
None indexed

EPSS Exploitation Probability

via FIRST.org ↗
6.6%probability of exploitation in next 30 days
Lower Risk93th percentile-13.78%
2.45%9.87%17.3%24.7%20.5%6.6%Dec 25Apr 26Jun 26

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

13 pkgs affected
.NETMicrosoft.AspNetCore.Http.NETMicrosoft.AspNetCore.App.NETMicrosoft.Owin.NETMicrosoft.AspNetCore.App.Runtime.linux-arm.NETMicrosoft.AspNetCore.App.Runtime.linux-arm64.NETMicrosoft.AspNetCore.App.Runtime.linux-musl-x64.NETMicrosoft.AspNetCore.App.Runtime.linux-x64.NETMicrosoft.AspNetCore.App.Runtime.osx-x64+5 more

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

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>

Affected Packages

13 total 13 fixed
EcosystemPackageVulnerable rangeFix
.NETNuGetMicrosoft.AspNetCore.Httpall versions2.1.22
.NETNuGetMicrosoft.AspNetCore.Appall versions2.1.22
.NETNuGetMicrosoft.Owinall versions4.1.1
.NETNuGetMicrosoft.AspNetCore.App.Runtime.linux-arm≥ 3.1.0&&< 3.1.83.1.8
.NETNuGetMicrosoft.AspNetCore.App.Runtime.linux-arm64≥ 3.1.0&&< 3.1.83.1.8
.NETNuGetMicrosoft.AspNetCore.App.Runtime.linux-musl-x64≥ 3.1.0&&< 3.1.83.1.8

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Microsoft.AspNetCore.Http. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. Fix

    Update Microsoft.AspNetCore.Http to 2.1.22 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-1045 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether CVE-2020-1045 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2020-1045. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

<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>
O3 Security · Impact-Aware SCA

Is CVE-2020-1045 in your dependencies?

O3 detects CVE-2020-1045 across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works