CVE-2026-103577 — Microsoft QUIC Security Feature Bypass Vulnerability

Executive Summary

Insecure default variable initialization in Microsoft QUIC allows an unauthorized attacker to bypass a security feature over a network.

Overview

7.5

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Security Feature Bypass

Weakness CWE-453: Insecure Default Variable Initialization

Released Oct 13 2026

Last Updated Oct 13 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

CVSS Vector

ATTACK VECTOR

Network

ATTACK COMPLEXITY

High

PRIVILEGES REQUIRED

None

USER INTERACTION

None

SCOPE

Changed

CONFIDENTIALITY

None

INTEGRITY

Low

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 6.5

EPSS Score

No EPSS score available for this CVE.

View on FIRST.org

Affected Products

14 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 11 Version 23H2 for ARM64-based Systems	`5126653 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 23H2 for x64-based Systems	`5126653 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5127648 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 24H2 for x64-based Systems	`5127648 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5127648 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 25H2 for x64-based Systems	`5127648 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5127646 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 version 26H1 for x64-based Systems	`5127646 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 26H2 for ARM64-based Systems	`5127648 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 26H2 for x64-based Systems	`5127648 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2022	`5126655 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2022 (Server Core installation)	`5126655 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2025	`5126646 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2025 (Server Core installation)	`5126646 (Security Update)`	Important	Security Feature Bypass	Yes

Patches

5 patches

Article	Type	Restart
`5126653`	Security Update	Yes
`5127648`	Security Update	Yes
`5127646`	Security Update	Yes
`5126655`	Security Update	Yes
`5126646`	Security Update	Yes

Exploits & PoC

No public exploit or PoC has been linked for this CVE yet. When available, references are sourced from public repositories and may be unverified or non-functional — review carefully before use.

Detection Rules

No public Sigma or Nuclei detection rule has been mapped to this CVE yet. Coverage is concentrated on exploited / high-profile vulnerabilities; check SigmaHQ for updates.

Acknowledgments

novice-22
PuH4ck3rX
Shibi Kishore N
Anonymous
Dr.-Ing Ashar Javed
Liang Zhu
Lucas Futures
Samuel

References

MSRC Advisory MITRE NVD