PatchTheCVECVE-2026-62815: Use after free in Microsoft QUIC allows an unauthorized attacker to execute code over a network.
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CRITICAL 9.8REMOTEWATCHLISTUPGRADEUPGRADEUPGRADE
CVE-2026-62815 is a critical-severity flaw (CVSS 9.8) affecting windows 11 23h2, windows 11 24h2, windows 11 25h2. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
Use after free in Microsoft QUIC allows an unauthorized attacker to execute code over a network.
Why this priority
- Critical severity
- CISA SSVC: automatable with total technical impact
- Remotely exploitable, no login, no user action
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 9.8 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 1.0% (top 38%) |
| CISA exploited list | No |
| Weakness | CWE-416 |
| Published | 2026-08-11 |
| Last modified | 2026-08-14 |
Publisher (CNA): Microsoft Corporation · Vendor: microsoft
Last updated 2026-08-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
microsoft windows 11 23h2 UPGRADE
Affected: < 10.0.22631.7517
Fixed in: 10.0.22631.7517
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows 11 24h2 UPGRADE
Affected: < 10.0.26100.9106
Fixed in: 10.0.26100.9106
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows 11 25h2 UPGRADE
Affected: < 10.0.26200.9106
Fixed in: 10.0.26200.9106
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows 11 26h1 UPGRADE
Affected: < 10.0.28000.2704
Fixed in: 10.0.28000.2704
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows server 2022 UPGRADE
Affected: < 10.0.20348.5440
Fixed in: 10.0.20348.5440
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows server 2025 UPGRADE
Affected: < 10.0.26100.33222
Fixed in: 10.0.26100.33222
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
Exact fixes by distribution
NuGet (.NET) · Microsoft.Native.Quic.MsQuic.OpenSSL · FIXED · 2.5.10 · vulnerable: >= 2.5.3, < 2.5.10 · source
dotnet add package Microsoft.Native.Quic.MsQuic.OpenSSL --version 2.5.10
NuGet (.NET) · Microsoft.Native.Quic.MsQuic.Schannel · FIXED · 2.5.10 · vulnerable: >= 2.5.3, < 2.5.10 · source
dotnet add package Microsoft.Native.Quic.MsQuic.Schannel --version 2.5.10
Fedora ELN · openbao · FIXED · 2.6.5-1.eln159 · FEDORA-2026-77adf886ae · source
sudo dnf upgrade --advisory=FEDORA-2026-77adf886ae
Fedora 46 · sugar-turtleart · FIXED · 220-16.fc46 · FEDORA-2026-b79483c788 · source
sudo dnf upgrade --advisory=FEDORA-2026-b79483c788
Install KB5120242 via Windows Update, then verify:
Get-HotFix -Id KB5120242
Windows Server 2022 (Server Core installation) · KB5120242 · FIXED · 10.0.20348.5499 · KB5120242 · source
Install KB5120242 via Windows Update, then verify:
Get-HotFix -Id KB5120242
Install KB5120229 via Windows Update, then verify:
Get-HotFix -Id KB5120229
Windows Server 2022 (Server Core installation) · KB5120229 · FIXED · 10.0.20348.5440 · KB5120229 · source
Install KB5120229 via Windows Update, then verify:
Get-HotFix -Id KB5120229
Windows Server 2025 (Server Core installation) · KB5120233 · FIXED · 10.0.26100.33296 · KB5120233 · source
Install KB5120233 via Windows Update, then verify:
Get-HotFix -Id KB5120233
Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-62815?
windows 11 23h2: upgrade to 10.0.22631.7517; windows 11 24h2: upgrade to 10.0.26100.9106; windows 11 25h2: upgrade to 10.0.26200.9106. Exact commands for each OS are on this page.
Is CVE-2026-62815 being exploited?
CVE-2026-62815 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-62815 affect?
CVE-2026-62815 affects windows 11 23h2, windows 11 24h2, windows 11 25h2. Severity is critical (CVSS 9.8). Use after free in Microsoft QUIC allows an unauthorized attacker to execute code over a network.
How urgent is CVE-2026-62815?
Priority 63/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist
Software pages
Windows vulnerabilities · Windows Server vulnerabilities
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