CVE-2026-78445: Use after free in Windows Services for NFS ONCRPC XDR Driver allows an unauthorized attacker to execute code o

Q: How do I fix CVE-2026-78445?

windows server 2012: mitigate or apply the listed mitigation; windows server 2016: upgrade to 10.0.14393.9512; windows server 2019: upgrade to 10.0.17763.9245. Exact commands for each OS are on this page.

Q: Is CVE-2026-78445 being exploited?

CVE-2026-78445 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-2026-78445 affect?

CVE-2026-78445 affects windows server 2012, windows server 2016, windows server 2019. Severity is critical (CVSS 9.8). Use after free in Windows Services for NFS ONCRPC XDR Driver allows an unauthorized attacker to execute code over a network.

Q: How urgent is CVE-2026-78445?

Priority 63/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTMITIGATEUPGRADEUPGRADE

CVE-2026-78445 is a critical-severity flaw (CVSS 9.8) affecting windows server 2012, windows server 2016, windows server 2019. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Use after free in Windows Services for NFS ONCRPC XDR Driver 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	2026-09-08
Last modified	2026-09-24

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-09-24 · 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
2026-09-24 23:19 UTCUpdated Record last modified

microsoft windows server 2012 MITIGATE

Affected: all versions · r2

Fixed in: no fixed release known

Safe to downgrade to: a release before r2

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 2016 UPGRADE

Affected: < 10.0.14393.9512

Fixed in: 10.0.14393.9512

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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora ELN · xfsdump · FIXED · 3.3.0-3.eln159 · FEDORA-2026-6e9bb3f901 · source

sudo dnf upgrade --advisory=FEDORA-2026-6e9bb3f901

Fedora 46 · fio · FIXED · 3.43-2.fc46 · FEDORA-2026-b36219886b · source

sudo dnf upgrade --advisory=FEDORA-2026-b36219886b

Windows Server 2019 · KB5122876 · FIXED · 10.0.17763.9245 · KB5122876 · source

Install KB5122876 via Windows Update, then verify: Get-HotFix -Id KB5122876

Windows Server 2019 (Server Core installation) · KB5122876 · FIXED · 10.0.17763.9245 · KB5122876 · source

Install KB5122876 via Windows Update, then verify: Get-HotFix -Id KB5122876

Windows Server 2022 · KB5122882 · FIXED · 10.0.20348.5622 · KB5122882 · source

Install KB5122882 via Windows Update, then verify: Get-HotFix -Id KB5122882

Windows Server 2022 (Server Core installation) · KB5122882 · FIXED · 10.0.20348.5622 · KB5122882 · source

Install KB5122882 via Windows Update, then verify: Get-HotFix -Id KB5122882

Windows Server 2025 (Server Core installation) · KB5122871 · FIXED · 10.0.26100.33438 · KB5122871 · source

Install KB5122871 via Windows Update, then verify: Get-HotFix -Id KB5122871

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-2026-78445?

windows server 2012: mitigate or apply the listed mitigation; windows server 2016: upgrade to 10.0.14393.9512; windows server 2019: upgrade to 10.0.17763.9245. Exact commands for each OS are on this page.

Is CVE-2026-78445 being exploited?

CVE-2026-78445 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-2026-78445 affect?

CVE-2026-78445 affects windows server 2012, windows server 2016, windows server 2019. Severity is critical (CVSS 9.8). Use after free in Windows Services for NFS ONCRPC XDR Driver allows an unauthorized attacker to execute code over a network.

How urgent is CVE-2026-78445?

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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References

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