Authentication Bypass in Apple macOS Screen Sharing
CISA: Apple macOS Improper Authentication Vulnerability
CVSS 3.1
9.8critical
EPSS
10%p95
Published
()
KEV added
AI analysis
CVE-2026-65400 is a critical (CVSS 9.8) improper authentication flaw (CWE-287) in Apple macOS's Screen Sharing service, caused by an authentication state-management defect. An attacker who can reach a vulnerable Mac's Screen Sharing service over the network can authenticate without valid credentials, gaining full remote access with high impact to confidentiality, integrity, and availability. All three currently supported macOS branches are affected: Sequoia, Sonoma, and Tahoe, in versions prior to the fixed releases. The flaw is being actively exploited on the internet, with public reporting that attackers use the bypass to deploy Monero cryptominers, and CISA added it to the Known Exploited Vulnerabilities catalog on 2026-08-18. EPSS estimates a 9.9% probability of exploitation within 30 days (95th percentile).
What to do: Upgrade to macOS Sequoia 15.7.9, macOS Sonoma 14.8.9, or macOS Tahoe 26.6.1 (or later) immediately; patching is mandatory for federal agencies under CISA BOD 26-04 given the KEV listing. As an interim mitigation, disable Screen Sharing or restrict it via firewall/VPN so VNC (port 5900) is not reachable from the internet. Review internet-exposed Macs for signs of compromise, especially unexplained Monero miner processes or abnormal CPU usage.
Affected
Apple macOS (Screen Sharing service)
supported macOS releases prior to the fixed builds listed below
Apple macOS Sequoia
all versions prior to 15.7.9
Apple macOS Sonoma
all versions prior to 14.8.9
Apple macOS Tahoe
all versions prior to 26.6.1
Estimated exposure
masson the order of 100M+ Macs run affected macOS versions; the directly exploitable subset is Macs with Screen Sharing enabled and internet-reachable — macOS's roughly 10-15% share of a desktop installed base exceeding one billion devices implies more than 100 million Macs on the affected branches, though only systems with the Screen Sharing/VNC service (port 5900) enabled and exposed to…
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
Description
An authentication issue was addressed with improved state management. This issue is fixed in macOS Golden Gate 27, macOS Sequoia 15.7.9, macOS Sonoma 14.8.9, macOS Tahoe 26.6.1, macOS Tahoe 26.7. An attacker on the network may be able to authenticate to Screen Sharing without valid credentials.
CISA Known Exploited Vulnerability
Affected
Apple macOS
Required action
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
CISA added four critical actively exploited flaws to KEV: macOS Screen Sharing, SharePoint, VMware vCenter, and Microsoft IKE, with APT and ransomware use.
CISA added CVE-2026-65400 (macOS Screen Sharing, CVSS 9.8), CVE-2026-55040 (SharePoint, CVSS 9.1), CVE-2026-59310 (VMware vCenter, CVSS 9.8) and CVE-2026-33824 (Microsoft IKE Service Extensions, CVSS 9.8) to the KEV catalog. The macOS flaw was abused to deliver a Monero miner, while the vCenter bug was exploited by a suspected China-nexus APT to install reverse_ssh backdoors and Babuk-derived ransomware across 361 victim IPs in 47 countries. Unit 42 linked CVE-2026-33824 to a Chinese-speaking actor running an AI-enabled campaign using DeepSeek. FCEB agencies must patch by August 21, 2026 under BOD 26-04.
Actively exploited CVE-2026-65400 in macOS Screen Sharing grants pre-auth root access; attackers deploy Monero miners on exposed systems.
NCSC-NL reported active exploitation of CVE-2026-65400 (CVSS 9.8), an authentication flaw in macOS Screen Sharing patched on August 6, 2026, with root access gained and a Monero miner planted on internet-exposed systems using port 5900. Related Screen Sharing bugs CVE-2026-43779, CVE-2026-43777, and CVE-2026-43760 were fixed in macOS Tahoe 26.6, and researcher @osxreverser noted a pre-auth flaw fixed alongside them affecting roughly 40,000 exposed hosts. Calif said an AI agent produced working exploits for both pre-auth bugs in four hours, underscoring the shrinking gap between patch release and weaponization.
CISA adds actively exploited flaws in Microsoft IKE, SharePoint, VMware vCenter, and macOS Screen Sharing to KEV catalog, due August 21.
CISA added four vulnerabilities to its Known Exploited Vulnerabilities catalog: CVE-2026-33824 (Windows IKE remote code execution, CVSS 9.8), CVE-2026-55040 (SharePoint JWT authentication bypass, CVSS 9.1), CVE-2026-59310 (VMware vCenter Syslog path traversal, CVSS 9.8), and CVE-2026-65400 (macOS Screen Sharing improper authentication). The SharePoint flaw combines four weaknesses including alg:none JWT forging to impersonate any user, with Defused researchers observing attackers using Rapid7's PoC against honeypots. The Dutch NCSC confirmed active exploitation of the macOS Screen Sharing flaw on August 15, 2026. Federal agencies must patch by August 21, 2026.
Dutch NCSC confirms active exploitation of critical macOS Screen Sharing flaw CVE-2026-65400, granting root access and installing Monero miners.
CVE-2026-65400 (CVSS 9.8) is an authentication state-management flaw in macOS's built-in Screen Sharing that lets network attackers authenticate without valid credentials. The Dutch NCSC confirmed active exploitation against systems with port 5900 exposed to the internet; in every documented case attackers obtained root access and installed a Monero cryptocurrency miner. Apple patched the bug in macOS Tahoe 26.6.1, Sequoia 15.7.9, and Sonoma 14.8.9, crediting Alfredo Pesoli of Bynario. A related researcher scan found roughly 40,000 exposed Screen Sharing hosts, and security firm Calif built working exploits for related flaws in about four hours using an AI coding agent.
CISA added four actively exploited vulnerabilities to its KEV catalog, headlined by CVE-2026-33824, a Windows IKE Service Extensions remote code execution flaw.
CISA's KEV addition, dated August 18, covers CVE-2026-33824 in Windows IKE Service Extensions, CVE-2026-55040 in on-premises Microsoft SharePoint Server, CVE-2026-59310 in Broadcom VMware vCenter, and CVE-2026-65400 in Apple macOS Screen Sharing. KEV listing confirms observed exploitation in the wild. Three of the four products are frequently deployed as high-value enterprise infrastructure, including remote-access endpoints and collaboration platforms.
Weekly recap: suspected China-nexus APT exploited VMware vCenter CVE-2026-59310, Lazarus used Windows zero-day CVE-2026-68820, and macOS flaw dropped Monero miners.
The week's top stories included a suspected China-nexus APT exploiting VMware vCenter CVE-2026-59310 (CVSS 9.8), a directory-traversal flaw enabling arbitrary code execution, with backdoors, reverse SSH and Babuk-derived ransomware deployed, per QUIRSO. NCSC-NL reported active exploitation of macOS Screen Sharing flaw CVE-2026-65400 (CVSS 9.8) to install Monero miners on systems with port 5900 exposed. Lazarus Group exploited Windows zero-day CVE-2026-68820 (CVSS 7.0) in Operation Dream Job, delivering ForestTiger and Troy backdoors to defense and aerospace targets. GeoServer patched a critical SQL injection flaw exploited within hours of disclosure, and Jamf analyzed the new Amnesia Stealer for macOS with live browser control.
CISA added actively exploited macOS flaw CVE-2026-65400 to its KEV catalog, affecting Tahoe, Sequoia, and Sonoma, with a patch deadline of August 21, 2026.
CISA acknowledged active exploitation of CVE-2026-65400, an authentication flaw affecting macOS Tahoe, Sequoia, and Sonoma, and added it to the Known Exploited Vulnerabilities Catalog. The vulnerability was discovered and reported to Apple by Alfredo Pesoli via Bynario Atlas. The remediation deadline is August 21, 2026.
Attackers actively exploit patched macOS Screen Sharing bug CVE-2026-65400 on systems with port 5900 exposed, gaining root to install a Monero cryptominer.
The Netherlands' National Cyber Security Centre (NCSC) reports active exploitation of CVE-2026-65400, an authentication flaw in macOS Screen Sharing that lets attackers authenticate without valid login credentials. Apple patched the issue in macOS Sequoia 15.7.9, Sonoma 14.8.9 and Tahoe 26.6.1, and the NCSC escalated its advisory on August 12 after proof-of-concept code went public and reports arrived of attacks on internet-exposed systems. In every reported case attackers obtained root access and installed a Monero crypto miner; users who cannot patch immediately are advised to disable Screen Sharing.
Apple's coordinated rollout patches 273 unique vulnerabilities across iOS 27, macOS Golden Gate 27, watchOS and Safari, including remote code execution flaws.
Apple shipped one of its largest coordinated security updates on September 14, 2026, fixing 273 unique CVEs across iOS 27, iPadOS 27, macOS Golden Gate 27, watchOS 27, tvOS 27, visionOS 27, Safari 27 and Xcode 27. Highlights include CVE-2026-65414, a Bluetooth out-of-bounds write enabling remote code execution, and CVE-2026-84607, an AVEVideoEncoder race condition granting kernel privileges to sandboxed apps. macOS Golden Gate 27 covers the broadest set with 210 CVEs, and Apple states none of the flaws were exploited in the wild.