CVE-2026-54990: Heap-based buffer overflow in Remote Desktop Client allows an unauthorized attacker to execute code over a net

Q: How do I fix CVE-2026-54990?

windows 11 24h2: upgrade to 10.0.26100.8875; windows 11 25h2: upgrade to 10.0.26200.8875; windows 11 26h1: upgrade to 10.0.28000.2269, 10.0.28000.2525. Exact commands for each OS are on this page.

Q: Is CVE-2026-54990 being exploited?

CVE-2026-54990 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-2026-54990 affect?

CVE-2026-54990 affects windows 11 24h2, windows 11 25h2, windows 11 26h1. Severity is critical (CVSS 9.8). Heap-based buffer overflow in Remote Desktop Client allows an unauthorized attacker to execute code over a network.

Q: How urgent is CVE-2026-54990?

Priority 62/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADEUPGRADEUPGRADE

CVE-2026-54990 is a critical-severity flaw (CVSS 9.8) affecting windows 11 24h2, windows 11 25h2, windows 11 26h1. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Heap-based buffer overflow in Remote Desktop Client 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	0.8% (top 43%)
CISA exploited list	No
Weakness	CWE-122
Published	2026-07-14
Last modified	2026-07-22

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-07-22 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-14 17:17 UTCPublished CVE record published
2026-07-22 16:18 UTCUpdated Record last modified

microsoft windows 11 24h2 UPGRADE

Affected: < 10.0.26100.8875

Fixed in: 10.0.26100.8875

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: < 10.0.26200.8875

Fixed in: 10.0.26200.8875

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: < 10.0.28000.2269 · < 10.0.28000.2525

Fixed in: 10.0.28000.2269, 10.0.28000.2525

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: < 10.0.26100.33158

Fixed in: 10.0.26100.33158

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

Fedora 46 · gcl · FIXED · 2.7.1-12.fc46 · FEDORA-2026-ff383a759b · source

sudo dnf upgrade --advisory=FEDORA-2026-ff383a759b

Fedora ELN · mozjs140 · FIXED · 140.13.0-5.eln159 · FEDORA-2026-f7ed0026e0 · source

sudo dnf upgrade --advisory=FEDORA-2026-f7ed0026e0

Windows Server 2025 (Server Core installation) · KB5099536 · FIXED · 10.0.26100.33158 · KB5099536 · source

Install KB5099536 via Windows Update, then verify: Get-HotFix -Id KB5099536

Windows Server 2025 · KB5099536 · FIXED · 10.0.26100.33158 · KB5099536 · source

Install KB5099536 via Windows Update, then verify: Get-HotFix -Id KB5099536

Windows 11 Version 25H2 for ARM64-based Systems · KB5101650 · FIXED · 10.0.26200.8875 · KB5101650 · source

Install KB5101650 via Windows Update, then verify: Get-HotFix -Id KB5101650

Windows 11 Version 25H2 for x64-based Systems · KB5101650 · FIXED · 10.0.26200.8875 · KB5101650 · source

Install KB5101650 via Windows Update, then verify: Get-HotFix -Id KB5101650

Windows 11 Version 24H2 for ARM64-based Systems · KB5101650 · FIXED · 10.0.26100.8875 · KB5101650 · source

Install KB5101650 via Windows Update, then verify: Get-HotFix -Id KB5101650

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-2026-54990?

windows 11 24h2: upgrade to 10.0.26100.8875; windows 11 25h2: upgrade to 10.0.26200.8875; windows 11 26h1: upgrade to 10.0.28000.2269, 10.0.28000.2525. Exact commands for each OS are on this page.

Is CVE-2026-54990 being exploited?

CVE-2026-54990 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-2026-54990 affect?

CVE-2026-54990 affects windows 11 24h2, windows 11 25h2, windows 11 26h1. Severity is critical (CVSS 9.8). Heap-based buffer overflow in Remote Desktop Client allows an unauthorized attacker to execute code over a network.

How urgent is CVE-2026-54990?

Priority 62/100. 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 · WinRM and RDP vulnerabilities

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References

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