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Remote Use-After-Free via QUIC Initial ALPN Handling

Critical
guhetier published GHSA-6w6v-mgp6-m93r Oct 13, 2026

Package

nuget Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet)

Affected versions

<2.5.12, <2.6.3

Patched versions

2.5.12, 2.6.3
nuget Microsoft.Native.Quic.MsQuic.Schannel (NuGet)
<2.5.12, <2.6.3
2.5.12, 2.6.3

Description

An unauthenticated attacker can trigger a use-after-free condition through crafted QUIC Initial packets targeting the ALPN handling path.

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-100219

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

CVE ID

CVE-2026-100219

Weaknesses

Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer. Learn more on MITRE.