Microsoft QUIC Use-After-Free Flaw Enables Remote Code Execution on Windows 11
An unauthorized attacker can execute code over a network via a critical use-after-free vulnerability in the Microsoft QUIC protocol on multiple Windows 11 versions.
Key points
- The flaw carries a CVSS score of 9.8, rated critical by the NVD.
- It affects Windows 11 versions 23H2 through 26H2 before specific build updates.
- The vulnerability allows remote code execution without prior authentication.
An attacker exploiting this flaw gains the ability to execute arbitrary code on a target system over a network. This access requires no prior authentication or user interaction, allowing an unauthorized remote actor to take control. The weakness resides within the Microsoft QUIC protocol implementation. Because the flaw is rated critical with a CVSS score of 9.8, it represents a severe risk to any exposed Windows 11 instance. As RedTeam Tribune reported previously on critical protocol flaws, such high-severity issues demand immediate attention from managed service providers.
How it unfolded
- The National Vulnerability Database recorded CVE-2026-100219 as a critical severity issue.
- The flaw was identified as a use-after-free error within the Microsoft QUIC component.
- Microsoft released specific build updates for affected Windows 11 versions to address the issue.
Who is affected
Microsoft Windows 11 Version 23H2 is affected if running builds prior to 10.0.22631.7652. Windows 11 Version 24H2 requires an update to build 10.0.26100.9711 or later to mitigate the risk. Users of Windows 11 Version 25H2 must update to build 10.0.26200.9711. Windows 11 Version 26H1 is vulnerable before build 10.0.28000.3231, while Version 26H2 needs build 10.0.26300.9711. Any system running these older builds is exposed to remote exploitation.
The fix
Microsoft has provided specific build updates for each affected Windows 11 version. Administrators should apply the respective cumulative updates to patch the vulnerability. Systems running the latest builds listed above are no longer affected by this specific CVE. No additional mitigation steps are required once the correct build is installed.
What made it possible
This incident relies on a memory management error known as use-after-free. Attackers exploit this by manipulating memory pointers that reference deallocated data. This technique typically serves the initial access stage of an intrusion, allowing remote code execution without authentication. Security teams usually monitor for anomalous network traffic patterns associated with protocol abuse. Check whether your endpoint detection tools are configured to flag unexpected memory access violations. Such controls help identify exploitation attempts before full system compromise occurs.
What to do and how to stay safe: Microsoft
- Inventory all Windows 11 devices to verify current build versions against the affected list.
- Prioritize patching for systems exposed to untrusted networks or the internet.
- Monitor network logs for unusual QUIC traffic patterns that may indicate exploitation attempts.
- Ensure endpoint detection and response tools are updated to recognize memory corruption behaviors.
Step-by-step guide: What Is Virtual Patching: How It Works Without Code Changes
General security guidance from the RedTeam Tribune newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
What is the CVSS score for CVE-2026-100219?
The National Vulnerability Database rates the vulnerability as critical with a CVSS score of 9.8.
Which Windows 11 versions are affected?
Versions 23H2, 24H2, 25H2, 26H1, and 26H2 are affected if they are running builds prior to the specified updates.
Does this flaw require user interaction?
No, the description states it allows an unauthorized attacker to execute code over a network without mentioning user interaction.
