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August updates trigger 0xc0000409 errors on Windows Server 2016
Microsoft says the August 2026 security update causes recurring CompatTelRunner.exe 0xc0000409 crashes on Windows Server 2016 with Compatibility Appraiser enabled; no functional impact.
Microsoft confirmed a known issue in which the August 2026 Windows security update generates recurring Application Error events (Event ID 1000, exception code 0xc0000409) in CompatTelRunner.exe on Windows Server 2016. The issue affects physical and virtual machines, including VMware and Azure environments, and per Microsoft does not affect device functionality. A permanent fix is planned for a future update, and the event log entries can be dismissed temporarily.
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Windows Remote Desktop Client Vulnerability Allows Attackers to Execute Remote Code
Microsoft patched CVE-2026-69485, an 8.8 CVSS RCE flaw in the Windows Remote Desktop Client affecting Windows 10/11 and Server 2016-2025.
Microsoft's September 2026 updates fix CVE-2026-69485, an Important-rated remote code execution vulnerability (CVSS 3.1: 8.8, temporal 7.7) in the Windows Remote Desktop Client caused by use of an uninitialized resource. An authenticated attacker with low privileges could send a specially crafted network request to execute code on an affected server, with no user interaction required. Microsoft says the flaw was not publicly disclosed before patching and rates exploitation as 'Less Likely' with no evidence of active exploitation. Affected products span Windows Server 2016, 2019, 2022 and 2025 and Windows 10 (1607-22H2) and Windows 11 (23H2-26H1), with fixes delivered via KBs including KB5123099, KB5122876 and KB5122882.
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Microsoft: September updates cause RDS failures on Windows Server
Microsoft confirms September 2026 Patch Tuesday updates break Remote Desktop Services on Windows Server 2012+; Group Policy mitigations and rollback workarounds available.
Microsoft confirmed that September 2026 Patch Tuesday security updates cause Remote Desktop Services failures on Windows Server 2012 and later, plus Windows 10 and Windows 11. Symptoms include unstable RDS, RDP connection failures after several minutes, sign-in issues, servers hanging at 'Please wait for the Remote Desktop Configuration,' and unresponsive MMC, RDS Licensing Diagnoser, and File Explorer. Microsoft published per-version Group Policy mitigations (covering KBs such as KB5124008, KB5122880, KB5122878, KB5122871, KB5122882, KB5122876, KB5123099, KB5123065, KB5123066) and suggests restarting affected VMs. Rolling back the updates restores RDS functionality but removes this month's security fixes.
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Microsoft security advisory – September 2026 monthly rollup (AV26-896) – Update 1
Canada's Cyber Centre relays Microsoft's September 2026 rollup; CISA added exploited zero-days CVE-2026-85880 and CVE-2026-81963 to KEV.
Advisory AV26-896 from the Canadian Centre for Cyber Security summarizes Microsoft's September 2026 monthly security rollup, listing affected products across Windows, Office, .NET, Azure, Exchange and SQL Server. It notes Microsoft confirmed CVE-2026-81963 and CVE-2026-85880 have been exploited. On September 8, 2026, CISA added both CVEs to its Known Exploited Vulnerabilities catalog, and administrators are urged to apply the updates.
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Urgent: Microsoft Issues Patches for 97 Flaws, Including Active Ransomware Exploit
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AD Rights Management Service (Part 1): Architecture, Deprecation, and Reconnaissance
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.
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Windows BitLocker Vulnerability Allows Attackers to Execute Malicious Code Remotely
Microsoft patched CVE-2026-69449, a heap-based buffer overflow in Windows BitLocker enabling code execution, affecting Windows 10/11 and Server 2012-2025 in September 2026 updates.
Microsoft disclosed CVE-2026-69449, a heap-based buffer overflow in Windows BitLocker rated Important, which could allow an authorized attacker to execute arbitrary code locally, with possible in-network exploitation via arbitrary endpoint calls. Microsoft rates exploitation as Less Likely and there was no public disclosure or in-the-wild exploitation at release. The flaw affects Windows 10 (1607-22H2), Windows 11 (23H2-26H1), and Windows Server 2012 through 2025, including Server Core. Fixes shipped in the September 2026 Patch Tuesday cumulative updates via platform-specific KBs such as KB5124012 and KB5122871.
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September 2026 Patch Tuesday roundup: Plugs for two zero day holes among almost 1,000 fixes in Windows
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.
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