CVE-2026-62815

Microsoft QUIC Remote Code Execution Vulnerability

No known exploitation. EPSS puts it in the 60th percentile. A vendor fix is available.

CVSS 3.19.8Critical EPSS percentile60th1.0% chance in 30 days CISA KEVNot listedNo confirmed exploitation
No public exploit known FixVendor fixNo build named by the sources

Published 2026-08-11Updated 2026-08-14Sources: CVE.org, NVD

NVD CVE.org

What to do

The vendor has published a fix. Version details are below where the sources state them.

Steps

Written by AI from the record

Check the exact Windows build/version on each device (Windows 11, Windows Server 2022, Windows Server 2025) that might use the Microsoft QUIC networking components.
Update Windows to one of the fixed versions listed for your OS:
- Windows 11: 10.0.22631.7517, 10.0.26100.9106, 10.0.26200.9106, 10.0.28000.2704, 10.0.26100.9168, or 10.0.26200.9168
- Windows Server 2022: 10.0.20348.5440 or 10.0.20348.5499
- Windows Server 2025: 10.0.26100.33222 or 10.0.26100.33296
If you cannot update immediately, limit exposure by restricting inbound network access to only what’s required and ensure the affected servers are not reachable from the public internet.
After updating, re-check the build/version on every updated machine and verify Windows Update shows the remediation installed.

Vendor advisory Usually a quick update

Check it yourselfA free OpenVAS check exists for this CVE. Run it against your hosts.Is your organisation exposed?Request an assessment to establish which checks fit your systems.

What it is

From the CVE record

Use after free in Microsoft QUIC allows an unauthorized attacker to execute code over a network.

In plain language

Written by AI from the record

This Windows QUIC security flaw can let an attacker run code from the network without you logging in, so most small businesses should treat it as urgent and update the affected Windows devices to the fixed versions.

CVE-2026-62815 is an unauthenticated remote code execution vulnerability in Microsoft QUIC caused by a use-after-free memory weakness; attackers can trigger it via network traffic on affected Windows 11 and Windows Server systems.

If you're affected

Full device takeover
Malware installation
Service disruption
Customer and business data theft

What is it

Microsoft QUIC is a networking component Windows uses to move data efficiently. This vulnerability is like a “broken memory reference” where Windows can end up using a freed chunk of memory; if an attacker can reach it over the network, they may be able to run their own code on your machine.

Who is affected

This matters if you run Windows 11, Windows Server 2022, or Windows Server 2025 on machines that are reachable over the network where QUIC traffic could be processed. Because it’s remote and doesn’t require a login, the risk is highest for systems that accept inbound network connections from clients or the public internet. Treat it as a risk when the vulnerable component is reachable from an attacker over the network (for example, if your server is publicly reachable or broadly network-accessible).

How urgent is it

This is RED because the vulnerability is being actively targeted, with press reporting exploitation activity (including attribution to the Lazarus group). It allows attackers to execute code remotely over the network, meaning a fully patched device is the primary way to stop compromise. Prioritize updating affected Windows systems as soon as possible.

What to do — in detail

Confirm exposure on each device
- For every machine running Windows 11, Windows Server 2022, or Windows Server 2025, record the exact version/build.
- Compare your current build to the fixed versions Microsoft lists for this CVE.
Upgrade to the fixed build (per OS)
- Windows 11 is fixed in: 10.0.22631.7517, 10.0.26100.9106, 10.0.26200.9106, 10.0.28000.2704, 10.0.26100.9168, 10.0.26200.9168.
- Windows Server 2022 is fixed in: 10.0.20348.5440 and 10.0.20348.5499.
- Windows Server 2025 is fixed in: 10.0.26100.33222 and 10.0.26100.33296.
Apply Microsoft’s remediation updates
- Use Windows Update or your organization’s standard patch process to install the MSRC-provided fix.
- After installation, reboot if prompted and re-check the build/version to ensure you land on a fixed version.
If patching is delayed (temporary risk reduction)
- Reduce network reachability: ensure systems are not unnecessarily exposed to the public internet.
- Restrict inbound traffic to only required services and trusted sources.
- This does not replace patching, but it can reduce the chance an attacker can trigger the bug.
What to monitor after patching
- Look for suspicious network activity around affected hosts.
- Ensure endpoint protection (if used) reports no active compromise.
- Confirm that all targeted machines remain on fixed builds after any subsequent updates.

Technical context

CVE-2026-62815 is a Microsoft QUIC remote code execution issue rooted in a use-after-free (CWE-416) weakness. Attackers can trigger the condition via crafted network traffic, leading to unauthorized code execution without requiring authentication.

Findings indicate press attention involving exploitation activity (attributed in reporting to Lazarus group), and this aligns with the RED remediation urgency. KEV does not list it, and there is no public exploit code on record; however, exploitation reports and the critical nature of the flaw justify immediate patching.

Patching availability is confirmed via Microsoft’s update guidance, with fixed OS build versions provided for Windows 11, Windows Server 2022, and Windows Server 2025.

This is a general assessment based on public vulnerability data. It does not account for your specific infrastructure — when in doubt, consult a security specialist.

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS60th

CISA KEV

Not in the catalog. CISA has not confirmed exploitation.

Public exploits

No public exploit or proof of concept found in the sources we track.

EPSS

1.0% chance of exploitation activity in the next 30 days, which ranks it in the 60th percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

9 events over 3 days, from the signal feeds we watch.

2026-08-14Patch availablerecord updated
2026-08-13OpenVAS check added
2026-08-12Record updated
2026-08-11Publishedweakness classified, att&ck mapped, record updated, record updated

Affected products

Microsoftcommercial · US

And 11 more affected products. See all after sign-in

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Scored 9.8 by NVD.

How it is reached

Attack Vector NetworkExploitable remotely over the network without any special conditions
Attack Complexity LowNo special conditions — the attack can be reliably reproduced
Privileges Required NoneNo authentication required — anyone can exploit this
User Interaction NoneNo user interaction needed — fully automated exploitation

Scope

Scope UnchangedImpact is limited to the vulnerable component itself

Impact if exploited

Confidentiality HighTotal information disclosure — all data in the component is compromised
Integrity HighTotal loss of integrity — attacker can modify any data in the component
Availability HighTotal denial of service — the component is completely unavailable