Microsoft's September Patch Tuesday fixed a record 974 flaws, including two Windows privilege-escalation zero-days actively exploited and added to CISA's KEV catalog.
Microsoft's September 2026 Patch Tuesday addressed a record 974 vulnerabilities (999 including 25 non-Microsoft CVEs), with over 110 rated critical; 723 affect Windows and 111 affect Office. Two Windows privilege-escalation zero-days are actively exploited: CVE-2026-85880, an ALPC heap-based buffer overflow, and CVE-2026-81963, an improper link resolution flaw in the Windows Update Stack, both allowing attackers to gain SYSTEM privileges. CISA added both flaws to its KEV catalog, giving federal civilian agencies until September 22, 2026 to apply fixes. Volexity, Proofpoint, MSTIC, and independent researchers were credited with the reports; notable additional fixes include network-reachable RCEs in Exchange, SharePoint, SQL Server, Remote Desktop Services, DNS, and DHCP.
Rapid7 published technical analysis of CVE-2026-63520, a remote code execution vulnerability in Microsoft SharePoint.
Rapid7 released an analysis covering CVE-2026-63520, a remote code execution flaw affecting Microsoft SharePoint. SharePoint is widely deployed in enterprise environments, making exposed, unpatched servers a likely target for exploitation. Defenders should consult the Rapid7 write-up for exposure checks and patch guidance. The available text does not confirm active exploitation at this time.
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.
Authentication Bypass in Apple macOS Screen Sharing
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).
· 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 KEVmass
Unauthenticated Double-Free RCE in Microsoft Windows IKE Extension
A double-free memory-corruption flaw (CWE-415) in the Microsoft Windows Internet Key Exchange (IKE) service extension allows a remote, unauthenticated attacker to trigger the bug with crafted network traffic, with no privileges or user interaction required. Successful exploitation yields remote code execution with full system impact, reflected in the critical 9.8 CVSS score (high confidentiality, integrity, and availability). The vulnerable IKE component is present in Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (23H2, 24H2, 25H2, 26H1), and Windows Server 2016, 2019, and 2022 (including 23H2), which ship it as a built-in feature. CISA added the flaw to the Known Exploited Vulnerabilities catalog on 2026-08-18, and security reporting confirms it is being actively exploited in the wild, though ransomware use is not yet confirmed. No public proof-of-concept is known, but the high EPSS score (72.7%, 99th percentile) signals a very strong likelihood of imminent or ongoing exploitation.
· Microsoft Windows 10 1607 · Microsoft Windows 10 1809 KEVmass
Unauthenticated Path Traversal RCE in Broadcom VMware vCenter Server Syslog
CVE-2026-59310 is a directory traversal (CWE-22) vulnerability in the Syslog server component of VMware vCenter Server, rated critical at CVSS 9.8. It can be triggered over the network without authentication or user interaction, allowing a malicious actor with network access to vCenter to achieve arbitrary code execution. An attacker who exploits it gains code execution on the vCenter appliance, and reported campaigns show it has been used to establish persistent remote access and, by a suspected China-nexus actor, to deploy Babuk ransomware. Any organization running an affected version of vCenter Server is exposed, especially where the management interface is reachable from the internet; the available data does not specify affected version ranges. Exploitation is confirmed in the wild: CISA added the flaw to its Known Exploited Vulnerabilities catalog on 2026-08-18, it was reportedly exploited just five days after disclosure, and EPSS estimates a 45.9% probability of exploitation within 30 days (99th percentile).
· Broadcom (VMware) vCenter Server KEV ransomwarelarge
Use-After-Free Privilege Escalation in Microsoft Windows ALPC
CVE-2023-21674 is a use-after-free flaw (CWE-416) in the Windows Advanced Local Procedure Call (ALPC) facility, the kernel-level mechanism Windows uses for fast communication between processes and system services. An attacker who can already run code on a Windows machine can trigger the bug by sending crafted ALPC requests, corrupting memory in a privileged process. Successful exploitation allows a local, low-privileged attacker to elevate to SYSTEM/administrator privileges, typically to gain full control of the host or to complete an exploit chain after an initial compromise. Essentially all supported Windows client and server installations from Microsoft are affected; the source data does not list specific versions, and the fix shipped with Microsoft's January 2023 Patch Tuesday, which addressed a record 974 vulnerabilities including this and one other actively exploited Windows zero-day. CISA added the CVE to the Known Exploited Vulnerabilities catalog on 2023-01-10, confirming exploitation in the wild; no public proof-of-concept is known, ransomware use is undetermined, and EPSS estimates a 41.8% probability of exploitation in the next 30 days (99th percentile).
Heap-Based Buffer Overflow in Windows ALPC Enables Local Privilege Escalation
CVE-2026-85880 is a heap-based buffer overflow in Windows Advanced Local Procedure Call (ALPC), the Windows mechanism for local inter-process communication. An authorized local attacker can trigger the overflow by submitting crafted input over ALPC, corrupting heap memory in the component that handles the request. Successful exploitation allows the attacker to execute code with elevated privileges, typically gaining SYSTEM-level control of the local host, which is especially valuable as a post-exploitation or sandbox-escape step. Affected products include Windows 10 (1607, 1809, 21H2, 22H2) and Windows Server 2012, 2016, 2019, and 2022, meaning most on-premises Windows estates are in scope. The flaw was fixed in Microsoft's record 974-CVE September 2026 Patch Tuesday and was added to CISA's KEV on 2026-09-08, confirming exploitation in the wild; press reports describe Windows zero-days being chained with a Chrome zero-day in 'BlueMoon' kit attacks, though the data does not explicitly confirm this CVE is the Windows flaw in that chain.
· Microsoft Windows 10 1607, 1809, 21H2, 22H2 · Microsoft Windows Server 2012, 2016, 2019, 2022 KEVmass
Local Privilege Escalation via Link Following in Windows Update Stack
CVE-2026-81963 is a link-following flaw (CWE-59, improper link resolution before file access) in the Microsoft Windows Update Stack, in which the component fails to correctly resolve file links before opening them. A local attacker with low privileges can plant or manipulate a link (symlink/junction) that the privileged update stack follows during operation, redirecting its file access to an attacker-controlled target. The result is local privilege escalation — CVSS 3.1 rates this 7.8 (high) with high confidentiality, integrity, and availability impact — allowing an authorized local user or malware already on the machine to gain elevated rights. Affected products are Windows 11 23H2, 24H2, 25H2, and 26H1 and Windows Server 2025; any unpatched system on those versions is exposed to any local account holder. The flaw was fixed in Microsoft's record September 2026 Patch Tuesday (974 CVEs), was added to CISA's KEV on 2026-09-08 as one of two Windows zero-days reported as exploited in the wild, and has no known public PoC or confirmed ransomware use.
· Microsoft Windows 11 23H2, 24H2, 25H2, 26H1 · Microsoft Windows Server 2025 KEVmass
CVE-2026-69730 is a use-after-free memory corruption flaw (CWE-416) in the Windows DNS service that allows an unauthenticated, remote attacker to execute arbitrary code by sending crafted network traffic to the affected system. Because the flaw is network-exploitable with no privileges or user interaction required (CVSS 3.1 9.8), any system running the vulnerable DNS service is a direct target. Successful exploitation would give the attacker code execution in the context of the DNS service, which on Windows Server typically runs with high privileges such as SYSTEM, and could enable wormable spread between vulnerable hosts. Affected organizations are those running the Windows DNS Server role — a component deployed on virtually all Windows Server domain controllers and on dedicated Windows DNS servers, especially those exposed to untrusted networks. As of the September 2026 Patch Tuesday release, there is no known public proof-of-concept, the flaw is not listed in CISA's KEV, and it has not been confirmed exploited in the wild, though it was flagged among roughly 20 'wormable' bugs and described in press coverage as a successor to the 2020 SigRed Windows DNS RCE.
· Microsoft Windows DNS Server role (Windows Server)mass
Use-After-Free RCE in Windows Remote Desktop Services
CVE-2026-69525 is a use-after-free memory corruption flaw (CWE-416) in Windows Remote Desktop Services, rated critical at CVSS 9.8. Per the CVSS vector, a remote, unauthenticated attacker can reach the vulnerable code path over the network with no privileges and no user interaction, presumably by sending crafted input to the RDP/RDS service. Successful exploitation yields remote code execution with high impact on confidentiality, integrity, and availability. Any Windows system running Remote Desktop Services is affected, and organizations exposing RDP (TCP 3389) to the internet are the primary concern, since public scans show millions of such endpoints. There is no public proof-of-concept or CISA KEV listing yet, and EPSS estimates a ~1.1% (63rd percentile) chance of exploitation within 30 days; the fix shipped as part of Microsoft's record 974-CVE Patch Tuesday, which separately included two exploited Windows zero-days and 20 wormable bugs.
Unauthenticated RCE in Microsoft SharePoint Server
CVE-2026-63520 is an improper input validation flaw (CWE-20) in Microsoft Office SharePoint, affecting on-premises SharePoint Server deployments. A remote, unauthenticated attacker can trigger the flaw by sending improperly validated input to the SharePoint service over the network; the high attack complexity (AC:H) indicates exploitation depends on specific conditions, but no privileges or user interaction are required. Successful exploitation results in arbitrary code execution on the server, with high impact to confidentiality, integrity, and availability — effectively full compromise of the SharePoint host. Organizations running self-hosted SharePoint Server are in scope; SharePoint Online/Microsoft 365 is not listed in the affected products. The issue is patched as of Microsoft's Patch Tuesday (headlines mark it FIXED), with Rapid7 analysis and a researcher-disclosed exploit chain available, but there is no public PoC, no CISA KEV listing, and no confirmed in-the-wild exploitation; EPSS puts exploitation probability at 2.9% (86th percentile).
· Microsoft SharePoint Server (Office SharePoint, on-premises)mass
Double Free Enables Unauthenticated RCE in Microsoft Exchange Server
CVE-2026-55007 is a double-free memory corruption flaw (CWE-415) in Microsoft Exchange Server in which the same heap allocation is freed twice, corrupting memory. A remote, unauthenticated attacker can trigger the flaw over the network, though the high attack complexity (AC:H) means reliable exploitation likely depends on favorable heap/timing conditions, making it harder to weaponize than typical pre-auth RCEs. Successful exploitation yields arbitrary code execution with high impact on confidentiality, integrity, and availability (CVSS 3.1: 8.1). Any organization running on-premises Microsoft Exchange Server is in scope, with the greatest risk on servers reachable from untrusted networks. As of now there is no public proof-of-concept, the flaw is not in CISA's KEV catalog, and EPSS estimates only a 0.7% chance of exploitation within 30 days; it was disclosed amid Microsoft's record September 2026 Patch Tuesday (974 CVEs), which press coverage highlighted for notable Exchange flaws.
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