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CVE-2026-62815 is a critical use-after-free vulnerability in Microsoft QUIC, Microsoft’s implementation of the QUIC transport protocol. QUIC is a modern UDP-based protocol that powers HTTP/3 traffic and is increasingly used throughout Windows networking components. The flaw exists in how the Microsoft QUIC stack handles memory management during connection processing.
The root cause is a use-after-free condition, where the QUIC implementation continues to reference memory that has already been freed. This occurs when the protocol stack improperly manages object lifecycles during QUIC connection handshakes or data transfer. An attacker can trigger this condition by sending specially crafted QUIC packets to a vulnerable system, causing the server to access freed memory. This memory corruption can be manipulated to execute arbitrary code.
The vulnerability is remotely exploitable over the network without authentication. An attacker does not need any special privileges or user interaction. The attack vector is network-based, and exploitation requires low complexity. If successfully exploited, an attacker gains the ability to execute arbitrary code on the target system with the privileges of the QUIC service. Successful exploitation leads to complete compromise of confidentiality, integrity, and availability.
Microsoft has confirmed active exploitation in the wild. The vulnerability is part of Microsoft’s August 2026 Patch Tuesday, which addressed 421 CVEs, with 62 rated Critical. CVE-2026-62815 carries a CVSS base score of 9.8 (Critical). The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Microsoft published the CVE on August 11, 2026, with the last modification on August 14, 2026.
DailyCVE Form:
Platform: Microsoft QUIC
Version: Windows 10/11/Server
Vulnerability: Use-After-Free RCE
Severity: 9.8 Critical
date: August 11, 2026
Prediction: Patch already released
What Undercode Say:
Check if system is vulnerable to CVE-2026-62815
Verify QUIC component versions
Get-WindowsOptionalFeature -Online -FeatureName "MSQuic"
Check installed updates for August 2026
Get-HotFix | Where-Object {$<em>.InstalledOn -gt (Get-Date).AddDays(-30)}
Verify specific patch for CVE-2026-62815
Get-HotFix -Id "KB504xxxx" Replace with actual August 2026 KB
Network monitoring for suspicious QUIC traffic patterns
Monitor UDP port 443 (QUIC) for anomalous packets
netsh trace start capture=yes provider=Microsoft-Windows-Kernel-Network tracefile=c:\quic_trace.etl maxsize=100
Query QUIC connection state
Get-NetTransportFilter -Protocol "UDP" | Where-Object {$</em>.LocalPort -eq 443}
Windows Event Logs for QUIC errors
Get-WinEvent -LogName "Microsoft-Windows-QUIC/Operational" | Where-Object {$_.LevelDisplayName -eq "Error"}
Audit QUIC service status
Get-Service -Name "MsQuic" | Select-Object Name, Status, StartType
Exploit: (Educational Purposes!)
The exploitation flow for CVE-2026-62815 follows a typical use-after-free pattern:
1. Trigger the free: Send a crafted QUIC packet that causes the target to free a specific memory object prematurely
2. Reclaim the memory: Immediately send additional packets that cause the target to allocate new data in the same memory location
3. Corrupt the pointer: The freed memory now contains attacker-controlled data, but the QUIC stack still holds a stale pointer
4. Execute the payload: When the QUIC stack dereferences the stale pointer, it jumps to attacker-controlled code
A proof-of-concept would involve:
Educational pseudo-code only - DO NOT USE MALICIOUSLY
import socket
import struct
Craft malicious QUIC packet with specific frame type that triggers UAF
def craft_quic_packet():
QUIC long header with crafted frame
packet = b'\xc0' + b'\x00' 10 Placeholder for real exploit
Frame that triggers object free
... actual exploit details are proprietary
return packet
Send to vulnerable target
target = ("192.168.1.100", 443)
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(craft_quic_packet(), target)
Protection:
- Immediately apply Microsoft’s August 2026 Patch Tuesday updates
- Block external QUIC traffic (UDP port 443) at perimeter firewalls until patched
- Disable QUIC protocol in affected applications if possible
- Enable Windows Defender Exploit Guard to mitigate use-after-free exploitation
- Monitor for suspicious QUIC traffic patterns and anomalous connection attempts
- Implement network segmentation to limit exposure of QUIC-enabled services
- Apply the specific patch referenced in DevGuard advisory (commit
1e6e999b)
Impact:
- Remote code execution with no authentication required
- Full compromise of confidentiality, integrity, and availability
- Affects all Windows systems with Microsoft QUIC enabled
- Active exploitation confirmed in the wild
- CVSS 9.8 Critical severity
- Part of August 2026 Patch Tuesday with 421 CVEs addressed
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Sources:
Reported By: nvd.nist.gov
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