CVE-2026-62901

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.WebSockets. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

An unchecked input for loop condition in .NET allows an unauthorized attacker to deny service over a network.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/428

CVSS Details

• Version: 3.1
• Severity: High
• Score: 7.5
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C
• Weakness: CWE-606: Unchecked Input for Loop Condition

Affected Platforms

• Platforms: Windows, Linux, macOS
• Architectures: All

<a name="affected-packages"></a>Affected Packages

The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below

<a name=".NET 10"></a>.NET 10

Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.NETCore.App.Runtime.win-arm64 | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.win-x64 | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.win-x86 | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.linux-arm | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.linux-arm64 | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.linux-musl-x64 | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.linux-x64 | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.osx-arm64 | >= 10.0.0, <= 10.0.10 | 10.0.11 Microsoft.NETCore.App.Runtime.osx-x64 | >= 10.0.0, <= 10.0.10 | 10.0.11

<a name=".NET 9"></a>.NET 9

Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.NETCore.App.Runtime.win-arm64 | >= 9.0.0, <= 9.0.18 | 9.0.19 Microsoft.NETCore.App.Runtime.win-x64 | >= 9.0.0, <= 9.0.18 | 9.0.19 Microsoft.NETCore.App.Runtime.win-x86 | >= 9.0.0, <= 9.0.18 | 9.0.19 Microsoft.NETCore.App.Runtime.linux-arm | >= 9.0.0, <= 9.0.18 | 9.0.19 Microsoft.NETCore.App.Runtime.linux-arm64 | >= 9.0.0, <= 9.0.18 | 9.0.19 Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 9.0.0, <= 9.0.18 | 9.0.19 Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 9.0.0, <= 9.0.18 | 9.0.19…

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 8.0.130 Runtime version: 8.0.30

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 8.0 to SDK 8.0.130 and Runtime 8.0.30 (JIRA:Rocky Linux-235468)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 8.0.130 Runtime version: 8.0.30

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 8.0 to SDK 8.0.130 and Runtime 8.0.30 [rhel-10.2.z] (JIRA:Rocky Linux-235472)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 10.0.111 Runtime version: 10.0.11

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 10.0 to SDK 10.0.111 and Runtime 10.0.11 (JIRA:Rocky Linux-235478)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 9.0.120 Runtime version: 9.0.19

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 9.0 to SDK 9.0.120 and Runtime 9.0.19 (JIRA:Rocky Linux-235473)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 8.0.130 Runtime version: 8.0.30

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 8.0 to SDK 8.0.130 and Runtime 8.0.30 [rhel-9.8.z] (JIRA:Rocky Linux-235471)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 9.0.120 Runtime version: 9.0.19

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 9.0 to SDK 9.0.120 and Runtime 9.0.19 [rhel-10.2.z] (JIRA:Rocky Linux-235477)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 9.0.120 Runtime version: 9.0.19

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 9.0 to SDK 9.0.120 and Runtime 9.0.19 [rhel-9.8.z] (JIRA:Rocky Linux-235476)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 10.0.111 Runtime version: 10.0.11

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 10.0 to SDK 10.0.111 and Runtime 10.0.11 [rhel-9.8.z] (JIRA:Rocky Linux-235481)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 10.0.111 Runtime version: 10.0.11

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)

• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)

• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)

• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 10.0 to SDK 10.0.111 and Runtime 10.0.11 [rhel-10.2.z] (JIRA:Rocky Linux-235482)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Unchecked input for loop condition in .NET allows an unauthorized attacker to deny service over a network.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 8.0.130
Runtime version: 8.0.30

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 8.0 to SDK 8.0.130 and Runtime 8.0.30 (JIRA:AlmaLinux-235468)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 8.0.130
Runtime version: 8.0.30

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 8.0 to SDK 8.0.130 and Runtime 8.0.30 [almalinux-10.2.z] (JIRA:AlmaLinux-235472)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 10.0.111
Runtime version: 10.0.11

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 10.0 to SDK 10.0.111 and Runtime 10.0.11 (JIRA:AlmaLinux-235478)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 9.0.120
Runtime version: 9.0.19

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 9.0 to SDK 9.0.120 and Runtime 9.0.19 (JIRA:AlmaLinux-235473)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 8.0.130
Runtime version: 8.0.30

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 8.0 to SDK 8.0.130 and Runtime 8.0.30 [almalinux-9.8.z] (JIRA:AlmaLinux-235471)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 9.0.120
Runtime version: 9.0.19

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 9.0 to SDK 9.0.120 and Runtime 9.0.19 [almalinux-10.2.z] (JIRA:AlmaLinux-235477)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 9.0.120
Runtime version: 9.0.19

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 9.0 to SDK 9.0.120 and Runtime 9.0.19 [almalinux-9.8.z] (JIRA:AlmaLinux-235476)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 10.0.111
Runtime version: 10.0.11

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 10.0 to SDK 10.0.111 and Runtime 10.0.11 [almalinux-9.8.z] (JIRA:AlmaLinux-235481)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a fast, lightweight and modular platform for creating cross platform applications that work on Linux, macOS and Windows. It particularly focuses on creating console applications, web applications and micro-services. .NET contains a runtime conforming to .NET Standards a set of framework libraries, an SDK containing compilers and a 'dotnet' application to drive everything.

SDK version: 10.0.111
Runtime version: 10.0.11

Security Fix(es):

• .NET: .NET Core: .NET Security Feature Bypass Vulnerability (CVE-2026-62899)
• .NET: .NET Information Disclosure Vulnerability (CVE-2026-62900)
• .NET: .NET Denial of Service Vulnerability (CVE-2026-62901)
• .NET: .NET Elevation of Privilege Vulnerability (CVE-2026-62909)

Bug Fix(es) and Enhancement(s):

• Update .NET 10.0 to SDK 10.0.111 and Runtime 10.0.11 [almalinux-10.2.z] (JIRA:AlmaLinux-235482)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Unchecked input for loop condition in .NET allows an unauthorized attacker to deny service over a network.

Unchecked input for loop condition in .NET allows an unauthorized attacker to deny service over a network.

Root has patched CVE-2026-62901 in the Microsoft.NETCore.App.Runtime.linux-musl-arm64 package for Root:NuGet. Multiple fixed versions available.

Miha Zupan discovered that .NET did not properly interpret certain HTTP requests. An attacker could possibly use this issue to perform request smuggling and bypass a security feature. (CVE-2026-62899)

Ivan Demchuk discovered that .NET did not properly handle the removal of sensitive information before storage or transfer. An attacker could possibly use this issue to disclose sensitive information. (CVE-2026-62900)

Kevin Gosse discovered that .NET did not properly check an input for a loop condition. An attacker could possibly use this issue to cause a denial of service. (CVE-2026-62901)

Kevin Gosse discovered that .NET did not properly perform error checking when securing shared resources used for diagnostics IPC. An attacker could possibly use this issue to elevate privileges. (CVE-2026-62909)