CVE-2020-1045 | 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>

Published: 2020-09-11 Last update: 2026-02-23 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-1045 is rated Moderate Risk (57.5/100): CVSS High severity, with high exploitation likelihood (EPSS 6.62%, 93th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2020-1045

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 20.40% 6.62% -13.78%
2 2026-03-03 20.52% 20.40% -0.12%
3 2025-11-21 — 20.52% —

Full EPSS history (23 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-1045

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2020-1045

GitHub Security Advisory for CVE-2020-1045

OS Trackers for CVE-2020-1045

vendor priority summary link
redhat high — https://access.redhat.com/security/cve/CVE-2020-1045

Affected software / configurations for CVE-2020-1045

Vendor Product Version Raw CPE
microsoft asp.net_core >= 2.1, <= 2.1.21 cpe:2.3:a:microsoft:asp.net_core:*:*:*:*:*:*:*:*
microsoft asp.net_core >= 3.1, < 3.1.8 cpe:2.3:a:microsoft:asp.net_core:*:*:*:*:*:*:*:*
fedoraproject fedora 32 cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
redhat enterprise_linux_aus 8.2 cpe:2.3:o:redhat:enterprise_linux_aus:8.2:*:*:*:*:*:*:*
redhat enterprise_linux_aus 8.4 cpe:2.3:o:redhat:enterprise_linux_aus:8.4:*:*:*:*:*:*:*
redhat enterprise_linux_aus 8.6 cpe:2.3:o:redhat:enterprise_linux_aus:8.6:*:*:*:*:*:*:*
redhat enterprise_linux_eus 8.2 cpe:2.3:o:redhat:enterprise_linux_eus:8.2:*:*:*:*:*:*:*
redhat enterprise_linux_eus 8.4 cpe:2.3:o:redhat:enterprise_linux_eus:8.4:*:*:*:*:*:*:*
redhat enterprise_linux_eus 8.6 cpe:2.3:o:redhat:enterprise_linux_eus:8.6:*:*:*:*:*:*:*
redhat enterprise_linux_tus 8.2 cpe:2.3:o:redhat:enterprise_linux_tus:8.2:*:*:*:*:*:*:*
redhat enterprise_linux_tus 8.4 cpe:2.3:o:redhat:enterprise_linux_tus:8.4:*:*:*:*:*:*:*
redhat enterprise_linux_tus 8.6 cpe:2.3:o:redhat:enterprise_linux_tus:8.6:*:*:*:*:*:*:*

References for CVE-2020-1045

cvelogic Threat Intelligence