CVE-2020-1045

HIGHNVD 7.57.5—

7.5

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.

CVSS v3: 7.5
EG Score: 7.5(medium)
EPSS: 95.6%
KEV: Not listed

Published

September 11, 2020

Last Modified

February 23, 2026

References (12)

secure@microsofthttps://access.redhat.com/errata/RHSA-2020:3699
secure@microsofthttps://github.com/dotnet/core/blob/main/release-notes/3.1/3.1.8/3.1.8.md#changes-in-318
secure@microsofthttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5LN2FUVBSVPGK7AU3NMLO3YR6CGONQPB/
secure@microsofthttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ASICXQXS4M7MTAF6SGQMCLCA63DLCUT3/
secure@microsofthttps://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1045
secure@microsofthttps://security.snyk.io/vuln/SNYK-RHEL8-DOTNET-1439600
af854a3a-2127-422b-91ae-364da2661108https://access.redhat.com/errata/RHSA-2020:3699
af854a3a-2127-422b-91ae-364da2661108https://github.com/dotnet/core/blob/main/release-notes/3.1/3.1.8/3.1.8.md#changes-in-318
af854a3a-2127-422b-91ae-364da2661108https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5LN2FUVBSVPGK7AU3NMLO3YR6CGONQPB/
af854a3a-2127-422b-91ae-364da2661108https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ASICXQXS4M7MTAF6SGQMCLCA63DLCUT3/
af854a3a-2127-422b-91ae-364da2661108https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1045
af854a3a-2127-422b-91ae-364da2661108https://security.snyk.io/vuln/SNYK-RHEL8-DOTNET-1439600

Patch Availability(2)

Vendor / Ecosystem	Fixed in / Patch	Released	Source
redhat	rh-dotnet31-dotnet-0:3.1.108-1.el7	2020-09-08	redhat
redhat	dotnet3.1-0:3.1.108-2.el8_2	2020-09-08	redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(13 across 1 ecosystem)

NuGet(13)

Package	Vulnerable range	Fixed in	Dependents
Microsoft.AspNetCore.App	2.1.0 ... 2.1.9 (25 versions)	2.1.22	—
Microsoft.AspNetCore.App.Runtime.linux-arm	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.App.Runtime.linux-arm64	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.App.Runtime.linux-musl-arm64	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.App.Runtime.linux-musl-x64	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.App.Runtime.linux-x64	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.App.Runtime.osx-x64	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.App.Runtime.win-arm	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.App.Runtime.win-arm64	3.1.5, 3.1.6, 3.1.7	3.1.8	—
Microsoft.AspNetCore.App.Runtime.win-x64	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.App.Runtime.win-x86	3.1.0 ... 3.1.7 (8 versions)	3.1.8	—
Microsoft.AspNetCore.Http	0.0.1-alpha ... 2.1.1 (22 versions)	2.1.22	—
Microsoft.Owin	1.1.0-beta1 ... 4.1.0 (21 versions)	4.1.1	—

All Vendor Advisories

(3)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 6× in last 7d / 6× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-05-27 13:39 UTCepss_batch
2026-05-26 23:14 UTCEG score recompute
2026-05-26 23:14 UTCVendor advisory
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-24 16:48 UTCepss_batch

Frequently asked(5)

What is CVE-2020-1045?

CVE-2020-1045 is a high vulnerability published on September 11, 2020. 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…

When was CVE-2020-1045 disclosed?

CVE-2020-1045 was first published in the National Vulnerability Database on September 11, 2020, with the most recent update on February 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2020-1045 actively exploited?

CVE-2020-1045 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 95.6% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2020-1045?

CVE-2020-1045 has a CVSS v3 base score of 7.5 (NVD).

How do I remediate CVE-2020-1045?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-1045, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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CVE-2020-1045

📅 Published

🔄 Last Modified

🔗 References (12)