A recently patched security flaw in Apple macOS is being actively exploited by hackers to bypass authentication, gain root access, and install a cryptominer, the Netherlands’ National Cyber Security Centre (NCSC) warns.
The vulnerability, tracked as CVE-2026-65400, , let attackers authenticate to macOS Screen Sharing without valid login credentials.
Apple fixed the issue with updates to macOS Sequoia (15.7.9), Sonoma (14.8.9), and Tahoe (26.6.1), and advised its macOS users to upgrade their systems.
“An authentication issue was addressed with improved state management,” Apple said in its advisory, crediting researcher Alfredo Pesoli, known as @__rev of Bynario Atlas, for reporting the issue.
On August 7, one day after Apple’s fix, the NCSC published its first advisory, urging organizations to update. The warning was informational, since no exploitation had been reported at that point. That changed five days later, on August 12, when the agency raised the advisory’s severity after proof-of-concept code went public and reports of active attacks on exposed systems began arriving.
“NCSC has received a report indicating active exploitation of this vulnerability has been observed on multiple systems where port 5900 was reachable from the internet. In all these cases, root access was obtained on the affected system and a Monero crypto miner was installed,” NCSC wrote.
Users who can’t patch immediately can disable Screen Sharing manually, by opening System Settings, selecting General, then Sharing, and switching the Screen Sharing toggle off.
NCSC hasn’t shared details on the scope of the attacks, including when they started, how many systems were hit, or whether attackers did anything beyond installing the cryptominer.