Microsoft Windows QUIC: Remote code execution via use-after-free
Summary
A use-after-free flaw in the Microsoft QUIC transport of Windows 11 and Windows Server allows an unauthenticated remote attacker to execute code. The attacker only needs to send crafted network traffic to an affected service that uses QUIC. The CVSS base score is 9.8 (critical), and the risk depends on whether QUIC services (UDP 443) are enabled and reachable from untrusted networks.
Affected
- Windows 11 version 23H2 (10.0.22631.0 to below 10.0.22631.7652)
- Windows 11 version 24H2 (10.0.26100.0 to below 10.0.26100.9711)
- Windows 11 version 25H2 (10.0.26200.0 to below 10.0.26200.9711)
- Windows 11 version 26H1 (10.0.28000.0 to below 10.0.28000.3231)
- Windows 11 version 26H2 (10.0.26300.0 to below 10.0.26300.9711)
- Windows Server 2022 (10.0.20348.0 to below 10.0.20348.5761)
- Windows Server 2025 including Server Core (10.0.26100.0 to below 10.0.26100.33650)
Fixed in
- Microsoft security update of October 2026 (Patch Tuesday, 13 October 2026)
- Fixed builds according to the CNA record: 10.0.22631.7652, 10.0.26100.9711, 10.0.26200.9711, 10.0.28000.3231, 10.0.26300.9711, 10.0.20348.5761 and 10.0.26100.33650 (Server 2025)
- A restart is required after installation
Workaround
Unknown. No vendor-documented workaround was found.
- Not from a source, own suggestion: if a host does not need QUIC, block inbound UDP 443 at the perimeter until it is patched. Confirm first that HTTP/3 and other required services are not affected.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact total.
- MSRC temporal vector E:U (exploit code maturity unproven).
- Belgium's CCB reports no public disclosure and no known exploitation.
- No public proof-of-concept found.
- A Tenable plugin reports an exploit as available, but its description is inconsistent; not confirmed.
Our recommendation
- Install the October 2026 cumulative update on all listed Windows 11 and Windows Server hosts, starting with internet-facing servers.
- Verify the fixed build numbers for each OS version in the MSRC product table before rollout.
- Identify hosts that listen on UDP 443 or run QUIC-based services and restrict their exposure.
- Monitor MSRC and CISA KEV for changes in exploitation status and for public proof-of-concept code.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-100219 msrc.microsoft.com
- Microsoft MSRC advisory CVE-2026-100219 msrc.microsoft.com
- CCB Belgium advisory on October 2026 Patch Tuesday ccb.belgium.be
- Action1: Patch Tuesday October 2026 www.action1.com
- Vicarius: Microsoft October 2026 Patch Tuesday www.vicarius.io
- Strix: CVE-2026-100219 www.strix.ai
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 30 Oct 2026, 18:57.
Original description (NVD)
Use after free in Microsoft QUIC allows an unauthorized attacker to execute code over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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