September 2026 Patch Tuesday updates cause Windows Server 2019/2022/2025 RDS sessions to freeze, forcing administrators to roll back.
Cumulative updates KB5122876 (Windows Server 2019), KB5122882 (2022), and KB5122871 (2025) trigger Remote Desktop Services freezes hours after boot, with RDP connections hanging at 'Connecting…' and Event ID 20498 logged. Administrators trace the fault to an apparent deadlock in RDPSERVERBASE!WDLIB_Close during session teardown; only hard resets restore service and the issue recurs. The same September release patched roughly 973 vulnerabilities, including two actively exploited zero-days (CVE-2026-81963, CVE-2026-85880, both in CISA's KEV) and a critical RDS RCE, CVE-2026-69525 (CVSS 9.8). Workarounds include DISM-based removal of the update or an unofficial FeatureManagement registry key disabling the suspected audio-redirection code path; Microsoft has not yet confirmed the bug.
September 2026 Windows Server cumulative updates cause Remote Desktop Services failures on Server 2019, 2022 and 2025, forcing some admins to roll back.
Admins report Remote Desktop Services failures after installing September 2026 Patch Tuesday updates KB5122876 (Server 2019), KB5122882 (Server 2022), and KB5122871 (Server 2025), with connections hanging, sessions failing after logout, and some systems requiring hard resets. One administrator debugging Server 2022 observed an apparent deadlock between RDP and the Local Session Manager, though Microsoft has not confirmed a root cause. Rolling back the updates restores RDS functionality but removes this month's security fixes. Microsoft had not responded to inquiries at publication time.
Researcher Chaotic Eclipse released FalconFlank, a PoC zero-day privilege escalation exploit against CrowdStrike Falcon's Microsoft Office macro removal feature.
Security researcher Chaotic Eclipse (also known as Nightmare Eclipse) published FalconFlank, a proof-of-concept zero-day exploit for a privilege escalation flaw in CrowdStrike Falcon Sensor. It abuses the Microsoft Office file malicious macro removal remediation feature, which runs with high privileges, and works on fully updated Windows 11 25H2 and Windows Server 2025 with Falcon Phase 3 Optimal Protection. CrowdStrike says it is investigating and advises customers to disable the Microsoft Office File Suspicious Macro Removal Windows policy. The same researcher recently released zero-day PoCs against Kaspersky Endpoint Security (HardBreacher) and Avast Antivirus (PrettyPrague), the latter dumping the SAM database for a SYSTEM shell.
Microsoft's September 2026 Patch Tuesday ships 964 fixes including two exploited Windows zero-days (CVE-2026-85880, CVE-2026-81963) and a wormable DNS RCE.
Microsoft's September 2026 Patch Tuesday includes 964 Microsoft vulnerabilities requiring customer action, a record attributed to AI-assisted bug discovery, plus 174 third-party/open-source and 23 Chromium/Edge CVEs. Two zero-days are exploited in the wild: CVE-2026-85880, a Windows ALPC heap overflow enabling AppContainer sandbox escape and privilege escalation, and CVE-2026-81963, a Windows Update Stack escalation to SYSTEM. CVE-2026-69730, an unauthenticated Windows DNS RCE, is not yet exploited but Microsoft expects exploitation, and roughly 20 bugs could be wormable. Separately, SAP issued a critical CVSS 10.0 fix for the EPP component used in S/4HANA and NetWeaver.
Huntress maps AD RMS architecture and recon paths, setting up an offline key-extraction attack against its unrotatable 255-year root key.
Huntress's multi-part research examines Active Directory Rights Management Services, Microsoft's enterprise DRM role that still ships in Windows Server 2025 despite migration guidance favoring Azure Information Protection. Part 1 covers the trust model and how an ordinary domain account can locate RMS clusters and read rights-policy templates. Part 2 will detail four independent paths for extracting the Server Licensor Certificate (SLC) private key via service-group membership and the configuration database, enabling fully offline decryption of protected documents. The SLC certificate is valid from 2002 to 2258 and has no key-rotation mechanism, so a stolen key decrypts protected content indefinitely.
Researcher NightmareEclipse published FalconFlank, a zero-day local privilege escalation in CrowdStrike Falcon Sensor abusing its Office malicious macro remediation feature.
A researcher known as Nightmare Eclipse published details of FalconFlank, a zero-day privilege escalation that abuses the Microsoft Office malicious macro removal feature in CrowdStrike Falcon Sensor, verified working on fully updated Windows 11 25H2 and Windows Server 2025 with Falcon Phase 3 Optimal Protection. CrowdStrike urged customers to disable the Office File Suspicious Macro Removal policy while it investigates, noting customers remain protected via Cloud Anti-malware for Microsoft Office Files; no CVE has been assigned. The same researcher previously released the Exploitarium dump of over 30 PoC exploits, and researcher Kevin Beaumont confirmed FalconFlank works.
Researcher Nightmare Eclipse released a PoC for FalconFlank, a privilege escalation zero-day in CrowdStrike Falcon's Office macro remediation feature.
Researcher Nightmare Eclipse published a zero-day PoC dubbed FalconFlank targeting CrowdStrike Falcon's Microsoft Office malicious macro removal feature, achieving privilege escalation on fully updated Windows 11 25H2 and Windows Server 2025 with Optimal Protection and macro removal enabled. Kevin Beaumont independently confirmed the exploit works. The same researcher also released HardBreacher, an elevation-of-privilege bug in Kaspersky Endpoint (since fixed via update), PrettyPrague, an Avast Sandbox flaw that dumps the SAM database for a SYSTEM shell (Gen Digital is developing a patch), and GreenSection, an Nvidia memory corruption bug that crashes systems. CrowdStrike advises customers to disable the Suspicious Macro Removal Windows policy while it investigates.
Researcher Chaotic Eclipse released ShieldBreak PoC, a claimed patch bypass for Microsoft Defender flaw CVE-2026-50656, now tracked as CVE-2026-69414.
Researcher Chaotic Eclipse released a PoC for ShieldBreak, a claimed full patch bypass of Microsoft Defender flaw CVE-2026-50656 (RoguePlanet), which can yield SYSTEM privileges. Independent researchers Kevin Beaumont and Will Dormann validated the exploit on Windows 11 25H2 and Windows Server 2025, noting it requires Defender to be enabled. Microsoft assigned CVE-2026-69414 (CVSS 7.8) with an 'Exploitation More Likely' assessment and is investigating, but has not yet released a patch. The article also notes CISA's KEV addition of the actively exploited Windows AFD.sys flaw CVE-2026-68820.
Researcher Chaotic Eclipse published a PoC bypassing Microsoft's CVE-2026-50656 Defender patch, enabling SYSTEM-level code execution on fully patched Windows systems.
Security researcher Chaotic Eclipse released a proof-of-concept for ShieldBreak, a Microsoft Defender zero-day that fully bypasses the patch for CVE-2026-50656 (RoguePlanet), a race condition in the Malware Protection Engine (mpengine.dll) allowing SYSTEM-level code execution. The PoC was tested on Windows 11 25H2 and Windows Server 2025 with a 100% success rate, and Windows 10 is also vulnerable though not supported by the PoC; the flaw may also leak 8 bytes of memory. Microsoft's MSRC had criticized the researcher's repeated uncoordinated disclosures, including YellowKey (BitLocker bypass), GreenPlasma, and LegacyHive (User Profile Service LPE).
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
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
Microsoft is aware of an elevation of privilege in the Microsoft Malware Protection Engine in Microsoft Defender publicly referred to as "RoguePlanet ".
Microsoft is aware of an elevation of privilege in the Microsoft Malware Protection Engine in Microsoft Defender publicly referred to as "RoguePlanet ".
Pre-auth use-after-free RCE in Microsoft Windows Deployment Services (WDS)
Microsoft Windows Deployment Services (WDS) contains a use-after-free memory-safety flaw (CWE-416) that an unauthenticated attacker can trigger by sending crafted network traffic to the WDS service, leading to remote code execution on the target system. The vulnerability affects Windows 10 1607 and 1809 and Windows Server 2012, 2016, 2019, 2022, and 2025 on systems where WDS is deployed, a role typically used for network-based (PXE) operating system imaging. A successful exploit grants the attacker code execution with high confidentiality, integrity, and availability impact, reflected in the critical CVSS 3.1 score of 9.8 with network vector, low complexity, and no privileges or user interaction required. No public proof-of-concept, CISA KEV listing, or confirmed in-the-wild exploitation is currently known, although EPSS estimates a 2.7% probability of exploitation within 30 days (85th percentile). The flaw was disclosed alongside Microsoft's record September 2026 Patch Tuesday, which shipped nearly 1,000 fixes including two Windows zero-days.
· microsoft Windows 10 1607 · microsoft Windows 10 1809large
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
Unauthenticated RCE in Microsoft Windows Routing and Remote Access Service (RRAS)
CVE-2026-69590 is a heap-based buffer overflow (CWE-122) in the Windows Routing and Remote Access Service (RRAS) that allows remote code execution, rated 9.8 Critical with a network attack vector requiring no privileges or user interaction. An attacker can trigger the flaw by sending crafted network traffic to a system running the RRAS service, and successful exploitation grants unauthorized access and code execution on the victim machine with high impact to confidentiality, integrity, and availability. Affected systems are Windows machines with the RRAS role/service enabled, typically servers used as VPN endpoints, routers, or NAT gateways; the specific affected Windows version ranges are not specified in the available data. The flaw was addressed in Microsoft's September 2026 Patch Tuesday release (September 8, 2026). There is no known exploitation in the wild, no public proof-of-concept, and it is not in CISA KEV, with EPSS estimating only a 1.0% chance of exploitation within 30 days (60th percentile).
· Microsoft Windows Routing and Remote Access Service (RRAS)large
Use-of-Uninitialized-Resource RCE in Microsoft Windows Remote Desktop Client
Microsoft's Windows Remote Desktop Client contains a use-of-uninitialized-resource flaw (CWE-908) that allows an authorized attacker to execute code over a network. Per the CVSS vector (AV:N/AC:L/PR:L/UI:N), exploitation requires the attacker to hold some level of authorization (low privileges) but involves no user interaction and low attack complexity, occurring while the client processes network session data. Successful exploitation yields code execution with high impact on confidentiality, integrity, and availability on the system running the RDP client. Because the Remote Desktop Client ships by default with Windows desktop and server editions, any Windows system used to initiate Remote Desktop connections is potentially affected, though the available data does not specify affected version ranges. There is currently no known exploitation, no public proof-of-concept, the flaw is not in CISA's KEV, and EPSS puts the 30-day exploitation probability at just 0.9%.
Local Elevation of Privilege in Microsoft Defender Malware Protection Engine
CVE-2026-69414, publicly dubbed 'ShieldBreak', is a high-severity (CVSS 3.1: 7.8) elevation-of-privilege flaw in the Microsoft Malware Protection Engine (MMPE) that powers Microsoft Defender, rooted in improper access control and improper privilege management (CWE-284/CWE-269). It is triggered locally: an attacker who already holds low privileges on the machine needs no user interaction (AV:L/AC:L/PR:L/UI:N) to trip the engine's flawed access checks, and successful exploitation yields high impact to confidentiality, integrity, and availability. News coverage reports public PoCs released under the 'ShieldBreak'/'ShieldCrash' names demonstrating SYSTEM-level access on Defender-protected Windows systems, including claims that the shipped patch can be bypassed and arbitrary files read as SYSTEM. Because MMPE ships as the scan engine inside Microsoft Defender, effectively every Defender-protected Windows 10/11 endpoint and server is potentially affected, though the source data specifies no affected engine version ranges. There is no confirmed in-the-wild exploitation (EPSS 0.6%, absent from CISA KEV), but given the public PoC claims, defenders should assume working exploit code exists.
· Microsoft Malware Protection Engine (used in Microsoft Defender)mass
Local Privilege Escalation via Link Following in Windows User Profile Service
CVE-2026-62832 is a local privilege escalation flaw (CWE-59, improper link resolution, or 'link following') in the Windows User Profile Service. An attacker who already holds a limited local account on an affected machine can cause the service to follow a symbolic link or junction before it validates file access, so the service performs file operations with elevated rights. Successful exploitation grants elevated privileges on the local system — typically up to administrator/SYSTEM level — with no user interaction required. Affected platforms include Windows 10 21H2 and 22H2, Windows 11 23H2 through 26H1, and Windows Server 2022 and 2025, which together span essentially the entire supported Windows estate. As of this analysis there is no public proof-of-concept, no CISA KEV listing, and no confirmed in-the-wild exploitation of this specific flaw; EPSS estimates a 3.3% (88th percentile) chance of exploitation within 30 days, although Microsoft's August 2026 Patch Tuesday fixed 400+ vulnerabilities and a separate zero-day (CVE-2026-68820) is under active attack.
· microsoft Windows 10 21H2 · microsoft Windows 10 22H2mass
Local Tampering via Link-Following Flaw in Windows 11 26H1 Container Isolation Driver
CVE-2026-72971 is a link-following flaw (CWE-59) in the Windows Container Isolation FS Filter Driver (unionfs.sys) on Windows 11 26H1: the driver performs file access without fully verifying that the path is not redirected through a symbolic link or junction. A local attacker who already holds low-privilege access (CVSS AV:L/PR:L, no user interaction required) can plant a malicious link at a location the driver processes, causing it to follow the link and act on an attacker-chosen target. The attacker gains tampering capability, which the CVSS scores as High integrity impact with no confidentiality or availability impact, meaning they can modify or overwrite files their account could not normally change. Any Windows 11 26H1 system is in scope per the CVE data, with the highest practical risk on shared or multi-user hosts and machines using container isolation features where unionfs.sys is active. No active exploitation is known: the CVE is not in CISA KEV, no public proof-of-concept exists, and EPSS puts 30-day exploitation probability at about 0.5%; the related news shows Microsoft's August 2026 Patch Tuesday shipped 400+ fixes, and defenders should confirm their devices received the unionfs.sys patch.
· microsoft Windows 11 26H1 (Container Isolation FS Filter Driver, unionfs.sys)mass
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