Microsoft's September 2026 Patch Tuesday fixes a record 974 CVEs, including two Windows zero-days exploited in the wild for privilege escalation.
Microsoft patched 974 vulnerabilities, its largest Patch Tuesday ever, including CVE-2026-85880, a heap buffer overflow in Windows ALPC allowing AppContainer sandbox escape to System, and CVE-2026-81963, a link-following flaw in the Windows Update Stack enabling local privilege escalation. Both were exploited as zero-days before the patch. ZDI's Dustin Childs says 20 of the fixed flaws are wormable, enabling unauthenticated remote code execution. The release also covers 723 Windows flaws and 222 Office bugs, plus fixes in Exchange, SharePoint, SQL Server, Azure and Exchange Server RCE (CVE-2026-55007).
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.
ZDI's September 2026 Microsoft update review lists two already-exploited Windows EoP zero-days and dozens of critical RCEs across Office, SQL Server, and Windows services.
The review catalogs Microsoft's September 2026 fixes, marking CVE-2026-85880 (Windows ALPC) and CVE-2026-81963 (Windows Update Stack) as already exploited elevation-of-privilege issues. It also lists critical RCE flaws in Office, Word, Excel, PowerPoint, Outlook, SQL Server, Windows DNS, DHCP and Failover Cluster, plus graphics component RCEs. Azure-side fixes include Entra ID, Copilot Studio, Azure AI Language and Azure AD B2C elevation-of-privilege flaws.
Microsoft's September 2026 Patch Tuesday fixes a record 964 CVEs, including two zero-days actively exploited in the wild.
Microsoft patched a record 964 CVEs in its September 2026 Patch Tuesday release, with 101 rated critical and 824 rated important, making it the largest Patch Tuesday to date. The release includes fixes for two zero-days that were exploited in the wild, with CVE-2026-81963 and CVE-2026-85880 highlighted in the release. Affected products span Windows core components, Office, Exchange, .NET, Visual Studio, Active Directory services (including AD CS and AD FS) and numerous Azure services. Tenable notes the release surpasses July's as the biggest ever.
Microsoft's September 2026 Patch Tuesday fixes 974 vulnerabilities across Windows and Office, including two actively exploited Windows privilege-escalation zero-days.
Microsoft's September 2026 Patch Tuesday addresses 974 vulnerabilities spanning Windows, Office, SQL Server, SharePoint, Exchange, Azure, and developer tools. Two Windows zero-days are confirmed exploited in attacks: CVE-2026-85880, a Windows ALPC elevation-of-privilege flaw, and CVE-2026-81963, a Windows Update Stack privilege-escalation flaw involving link following. The release also includes Critical fixes for Windows Secure Kernel Mode, VBS Enclave, Excel, and Word.
ZDI disclosed an HTML injection flaw in Microsoft Office (CVSS 7.6) that lets remote attackers disclose sensitive information via malicious pages or files.
Zero Day Initiative advisory ZDI-26-607 describes an HTML injection vulnerability in Microsoft Office that leads to information disclosure. Remote attackers need the target to visit a malicious page or open a malicious file to trigger it. ZDI rated the issue 7.6 on the CVSS scale and the advisory lists no CVE identifier. The advisory does not indicate active exploitation.
Fancy Bear (APT28) is reported exploiting a Microsoft Office flaw, per Infosecurity Magazine; details unavailable.
Infosecurity Magazine reports that Fancy Bear (APT28), the Russian state-sponsored threat group, is exploiting a Microsoft Office flaw. The article text was unavailable, so details on the specific CVE, affected versions, and victimology are not provided.
Microsoft's August Patch Tuesday delivers fixes for 400 security vulnerabilities across its product lineup.
Microsoft released its August Patch Tuesday security updates, fixing 400 vulnerabilities, described as another massive monthly batch. The source text provides no breakdown of severity classes, affected products, or whether any flaws were actively exploited. Defenders should prioritize patching based on Microsoft's exploitation status ratings in the official bulletin.
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
Missing Authorization in Microsoft Entra ID Enables Privilege Escalation
CVE-2026-83941 is a missing-authorization flaw (CWE-862) in Microsoft Entra ID, the cloud identity service behind Microsoft 365 and Azure. An already-authenticated, low-privileged user can send a network request to an Entra ID endpoint that fails to enforce proper authorization checks, requiring no user interaction. Exploitation lets the attacker elevate their privileges within the directory, with high confidentiality and integrity impact (CVSS 9.9, scope changed). Any organization that uses Microsoft Entra ID is in the affected population. The flaw was patched in Microsoft's September 2026 Patch Tuesday release; it is not in CISA KEV, has no known public proof-of-concept, and carries a low EPSS of roughly 0.7%.
Heap Buffer Overflow in Microsoft Excel Allows Local Code Execution (CVE-2026-81959)
CVE-2026-81959 is a heap-based buffer overflow (CWE-122) in Microsoft Office Excel, with an associated integer overflow/wraparound (CWE-190) that Microsoft notes as part of the flaw. Because the attack vector is local and requires user interaction, exploitation requires a user to open a specially crafted spreadsheet file in an affected Excel or Office installation, for example one delivered via email or downloaded from an untrusted source. Successful exploitation allows an unauthorized attacker to execute arbitrary code in the context of the current user, with high impact on confidentiality, integrity, and availability on the victim machine. Anyone running Excel in Microsoft 365 Apps or perpetual Office 2016, 2019, 2021, or 2024 is affected. The flaw was addressed in Microsoft's September 2026 Patch Tuesday (a release covering 974 vulnerabilities); it is not in CISA KEV, no public proof-of-concept is known, and EPSS puts 30-day exploitation probability at just 0.4%, so no confirmed in-the-wild exploitation is known.
Stack-Based Buffer Overflow in Microsoft Excel Allows Local Code Execution
Microsoft has fixed a stack-based buffer overflow (CWE-121) in Microsoft Office Excel that allows an unauthorized local attacker to execute arbitrary code. Given the CVSS vector (local attack vector, no privileges required, user interaction required), exploitation most plausibly requires a user to open a specially crafted spreadsheet, for example delivered via email or a shared location. Successful exploitation yields code execution in the context of the user who opened the file, with high impact on confidentiality, integrity and availability. Anyone running Excel — including Microsoft 365/365 Apps and the perpetual Office 2016, 2019, 2021 and 2024 releases — is affected, and the fix shipped in the September 2026 Microsoft Patch Tuesday release. There is no known public proof of concept, the issue is not in CISA's KEV catalog, and EPSS estimates only a 0.4% probability of exploitation in the next 30 days.
· microsoft Excel · Microsoft 365 affected builds as addressed in Microsoft's September 2026 security updatemass
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).
Authentication Bypass in Microsoft Entra ID Enables Privilege Elevation
CVE-2026-62916 is an authentication bypass (CWE-288) in Microsoft Entra ID, Microsoft's cloud identity and access management service, in which an alternate path or channel allows authentication checks to be circumvented. Per the CVSS vector, it is exploitable remotely over a network with no privileges and no user interaction required, by authenticating via an alternate path instead of the standard sign-in flow. A successful unauthenticated attacker gains the ability to elevate privileges, with high impact on confidentiality, integrity, and availability reflected in the 9.8 critical score. The affected population includes organizations relying on Entra ID, which is the default identity platform for Microsoft 365, Azure, and hybrid deployments; the available data does not specify affected versions or the specific sub-component involved. There is no public proof-of-concept, no confirmed in-the-wild exploitation, and the CVE is not in CISA's KEV; EPSS assigns a 0.6% probability of exploitation within 30 days.
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.
Heap-based Buffer Overflow in Microsoft Excel Enables Local Code Execution
CVE-2026-81951 is a heap-based buffer overflow (CWE-122) in Microsoft Excel, the spreadsheet component of Microsoft Office and Microsoft 365. Per the CVSS vector (AV:L with UI:R and no privileges required), exploitation requires user interaction, most plausibly a user opening a crafted spreadsheet, rather than any network-reachable service. Successful exploitation lets an unauthorized attacker execute arbitrary code locally, with the CVSS scoring high impact on confidentiality, integrity, and availability. All supported Excel-bearing releases are affected: Microsoft 365 Apps/Microsoft 365, Office 2016, Office 2019, Office 2021, and Office 2024. No public proof of concept is known, the flaw is not in CISA's KEV, and EPSS estimates only a ~0.4% chance of exploitation within 30 days, indicating no known in-the-wild exploitation as of the September 2026 Patch Tuesday that shipped the fix.
Query Logic Flaw Enables Info Disclosure in Microsoft Discovery Studio
CVE-2026-62906 is an improper neutralization of special elements in data query logic (CWE-943, an SQL-injection-style flaw) in Microsoft Discovery Studio that allows an unauthorized attacker to disclose information over a network. It is remotely exploitable without authentication (AV:N/PR:N) but requires user interaction (UI:R), meaning a user must perform some action, such as clicking a crafted link or submitting crafted input, for the attack to succeed. Successful exploitation has a high impact on confidentiality, potentially exposing sensitive data, while integrity and availability are unaffected. Any organization running Microsoft Discovery Studio is potentially affected, and Microsoft addressed the issue as part of the September 2026 Patch Tuesday security updates. There is currently no known public proof-of-concept, no inclusion in CISA's Known Exploited Vulnerabilities catalog, and EPSS estimates only a 0.7% probability of exploitation in the next 30 days, so no active exploitation is known at this time.
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