CVE-2026-78450: Use after free in Reliable Multicast Transport Driver (RMCAST) allows an unauthorized attacker to execute code

Q: How do I fix CVE-2026-78450?

windows 10 1809: upgrade to 10.0.17763.9245; windows server 2019: upgrade to 10.0.17763.9245; windows server 2022: upgrade to 10.0.20348.5622. Exact commands for each OS are on this page.

Q: Is CVE-2026-78450 being exploited?

CVE-2026-78450 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-78450 affect?

CVE-2026-78450 affects windows 10 1809, windows server 2019, windows server 2022. Severity is high (CVSS 8.1). Use after free in Reliable Multicast Transport Driver (RMCAST) allows an unauthorized attacker to execute code over a network.

Q: How urgent is CVE-2026-78450?

Priority 52/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

This month

HIGH 8.1REMOTEWATCHLISTUPGRADEUPGRADEUPGRADE

CVE-2026-78450 is a high-severity flaw (CVSS 8.1) affecting windows 10 1809, windows server 2019, windows server 2022. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Use after free in Reliable Multicast Transport Driver (RMCAST) allows an unauthorized attacker to execute code over a network.

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 47%)
CISA exploited list	No
Weakness	CWE-416
Published	2026-09-08
Last modified	2026-09-16

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-09-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-08 18:20 UTCPublished CVE record published
2026-09-16 20:30 UTCUpdated Record last modified

microsoft windows 10 1809 UPGRADE

Affected: < 10.0.17763.9245

Fixed in: 10.0.17763.9245

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 2019 UPGRADE

Affected: < 10.0.17763.9245

Fixed in: 10.0.17763.9245

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: < 10.0.20348.5622

Fixed in: 10.0.20348.5622

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: < 10.0.26100.33438

Fixed in: 10.0.26100.33438

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.

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.

Quick answers

How do I fix CVE-2026-78450?

windows 10 1809: upgrade to 10.0.17763.9245; windows server 2019: upgrade to 10.0.17763.9245; windows server 2022: upgrade to 10.0.20348.5622. Exact commands for each OS are on this page.

Is CVE-2026-78450 being exploited?

CVE-2026-78450 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-2026-78450 affect?

CVE-2026-78450 affects windows 10 1809, windows server 2019, windows server 2022. Severity is high (CVSS 8.1). Use after free in Reliable Multicast Transport Driver (RMCAST) allows an unauthorized attacker to execute code over a network.

How urgent is CVE-2026-78450?

Priority 52/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Windows vulnerabilities · Windows Server vulnerabilities

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References

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