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Install the latest macOS security update Apple offers for your Mac. Apple’s August 6, 2026 advisories list fixes for CVE-2026-65400 in macOS Tahoe 26.6.1, Sequoia 15.7.9 and Sonoma 14.8.9; those versions are patch reference points, not a guarantee they remain the newest releases. If you do not need Screen Sharing, turn it off, and make sure port 5900 is not reachable from the public internet. If this is a work Mac, ask IT to verify its update and exposure status.
What is the Mac Screen Sharing security flaw?
Apple says a network attacker may be able to authenticate to macOS Screen Sharing without valid credentials. The vulnerability is tracked as CVE-2026-65400. Apple says it fixed the authentication issue through improved state management.
Apple credits Alfredo Pesoli (@__rev) via Bynario Atlas. The Apple advisories identifying the fixes for Tahoe, Sequoia and Sonoma were published August 6, 2026:
- macOS Tahoe 26.6.1 security content
- macOS Sequoia 15.7.9 security content
- macOS Sonoma 14.8.9 security content
The Netherlands National Cyber Security Centre (NCSC) reports active exploitation in incidents where Screen Sharing was enabled and port 5900 was reachable from the internet. In those observed cases, attackers obtained root access and installed Monero-mining software. That report does not mean every Mac is compromised, or that enabling Screen Sharing by itself makes every Mac publicly accessible. The NCSC lists the vulnerability at CVSS v3 7.1 in its Security Advisory NCSC-2026-0280 revision 1.0.1.
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What to do to protect your Mac
1. Install the latest security update Apple offers
Use Software Update to check for and install the latest macOS update available for your Mac. The versions in Apple’s advisories—Tahoe 26.6.1, Sequoia 15.7.9 and Sonoma 14.8.9—are the releases those advisories say contain the fix, all published August 6, 2026. Check Apple’s current update offering rather than treating those numbers as a claim about the newest releases today. The Netherlands NCSC advises organizations to install available Apple updates as soon as possible.
2. Disable Screen Sharing if you do not use it
If you have no need to let another person access your Mac through Screen Sharing, turn the feature off. The NCSC’s reported exploitation cases involved Screen Sharing being enabled. Apple’s security advisories explain the flaw and patch but do not provide a consumer-facing settings path, so use Apple’s current setup guidance for the exact controls on your macOS version rather than relying on an assumed menu path.
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3. Check whether port 5900 is exposed to the internet
The NCSC says port 5900 was reachable from the internet in the exploitation cases it observed. A feature being enabled does not by itself establish that the port is publicly reachable; exposure depends on the network setup. If you manage your own network, verify that port 5900 cannot be reached from the public internet. On a work or managed Mac, ask IT to check rather than changing network or firewall settings yourself.
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If you are unsure whether Screen Sharing is in use, or whether a Mac has been updated and its port exposure checked, contact your IT department or service provider. The Netherlands NCSC specifically advises users who do not know whether they use Screen Sharing to ask IT or their provider to apply updates and check security. Its macOS Screen Sharing alert was published August 7, 2026 and updated August 13, 2026.
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How to assess the immediate risk
The practical checks are whether the Mac has received Apple’s applicable security update, whether Screen Sharing is enabled, and whether port 5900 is reachable from the public internet. The NCSC’s account connects observed exploitation to the combination of enabled Screen Sharing and internet-reachable port 5900. If you find that combination, prioritize applying Apple’s available update and have the exposure addressed; for an organizational Mac, involve IT.
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