Microsoft's September 2026 Patch Tuesday delivers a record patch count, fixing two exploited zero-days and a wormable DNS flaw dubbed a SigRed successor.
Microsoft's September 2026 Patch Tuesday sets another record patch count, fixing two vulnerabilities exploited as zero-days: CVE-2026-81963, a Windows Update Stack low-privilege-to-SYSTEM escalation reported by MSTIC, and CVE-2026-85880, a Windows Advanced Local Procedure Call escalation reported by Proofpoint. Zero Day Initiative's Dustin Childs urges priority on a cluster of 20 potentially wormable bugs including DNS RCE CVE-2026-69730, described as a spiritual successor to SigRed, plus Kerberos authentication bypass CVE-2026-69676 that could give any authenticated domain user RCE on domain controllers, and Exchange RCE CVE-2026-55007 via a malicious Visio attachment. All Windows fixes are bundled in cumulative updates, and experts stress prioritizing exploitable, reachable flaws over raw patch counts.
Microsoft's September 2026 Patch Tuesday fixes a record 966 flaws, including two Windows zero-days actively exploited to gain SYSTEM privileges.
Microsoft's September 2026 Patch Tuesday addresses a record 966 vulnerabilities, including 105 rated Critical, 81 of them remote code execution bugs. Two zero-days were actively exploited: a Windows Update Stack link-following flaw and a Windows ALPC heap-based buffer overflow, both allowing local elevation to SYSTEM privileges. The ALPC flaw was reported by Volexity and Proofpoint researchers, while the Update Stack flaw was credited to Romain Deperne and the Microsoft Threat Intelligence Centre. Microsoft shared no details on how the flaws were exploited in attacks.
Kerberos Capture-Replay Authentication Bypass in Microsoft Windows (RCE)
CVE-2026-69676 is a capture-replay authentication bypass (CWE-294) in the Windows Kerberos implementation, disclosed by Microsoft as part of the September 2026 Patch Tuesday. An attacker who is already authorized (low-privilege credentials) can replay captured authentication material over the network to bypass authentication checks. Successful exploitation results in remote code execution, with high impact on confidentiality, integrity, and availability (CVSS 3.1 score of 8.8). Any organization running Windows in an Active Directory environment is potentially affected, since Kerberos is the default authentication protocol for Windows domains. As of this analysis there is no known public proof-of-concept, the flaw is not in CISA's KEV catalog, and EPSS estimates only a ~1.2% chance of exploitation within 30 days, though it shipped in a record-sized Patch Tuesday release alongside two actively exploited zero-days.
· Microsoft Windows (Kerberos authentication implementation)mass
Use-After-Free Remote Code Execution in Microsoft Active Directory Domain Services
CVE-2026-69524 is a use-after-free memory corruption flaw (CWE-416) in Microsoft's Active Directory Domain Services (AD DS), patched as part of Microsoft's September 2026 Patch Tuesday release. An unauthorized attacker with no privileges or user interaction can trigger the flaw remotely over the network, though the high attack-complexity rating suggests reliable exploitation may depend on favorable memory or timing conditions. A successful exploit yields remote code execution on the target, with high impact to confidentiality, integrity, and availability — typically a domain controller holding an organization's central authentication data. Any organization running Windows Server with the AD DS role enabled (i.e., operating domain controllers) is affected. As of this data there are no known in-the-wild exploits, no public proof of concept, and a modest 0.7% EPSS probability of exploitation within 30 days.
· Microsoft Windows Server with Active Directory Domain Services (AD DS) rolemass
Use-After-Free RCE in Microsoft Active Directory Domain Services
CVE-2026-69546 is a use-after-free (CWE-416) memory corruption flaw in Microsoft's Active Directory Domain Services (AD DS), the directory service role that runs on Windows Server domain controllers. It can be triggered over the network by an unauthenticated attacker, although the high attack-complexity metric suggests exploitation requires favorable timing or conditions rather than a simple, repeatable request. Successful exploitation yields remote code execution on the domain controller with the confidentiality, integrity, and availability of the host all rated high, which in practice risks compromise of the identity infrastructure that underpins the entire domain. Any organization running the AD DS role on Windows Server is affected; the exact server builds are enumerated in Microsoft's September 2026 security updates. As of now there is no public proof-of-concept, the flaw is not in CISA's KEV catalog, and EPSS assigns it roughly a 0.7% chance of exploitation within 30 days.
· Microsoft Active Directory Domain Services (AD DS) on Windows Servermass
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.
Missing-Authorization Local Privilege Escalation in Microsoft Data Sharing Service Client
CVE-2026-73014 is a missing authorization flaw (CWE-862) in the Data Sharing Service Client, a Microsoft component assigned by the Microsoft CNA. A local attacker who already holds a low-privileged authorized account on the machine can invoke the service without a required authorization check and elevate privileges. Successful exploitation yields high impact to confidentiality, integrity, and availability (CVSS 7.8), which typically means gaining elevated rights on the local system. Any system running the affected component is exposed, though the attack requires local access and is not remotely exploitable. There is no known public proof-of-concept, it is not in CISA KEV, and EPSS puts 30-day exploitation probability at just 0.3%; the fix shipped in Microsoft's September 2026 Patch Tuesday, which addressed 966 flaws.
Unauthenticated out-of-bounds read DoS in Microsoft Windows BranchCache
CVE-2026-69329 is an out-of-bounds read (CWE-125, arising from an integer-overflow condition, CWE-190) in the BranchCache component of Microsoft Windows. A remote, unauthenticated attacker can trigger the flaw over the network with no privileges or user interaction by sending malformed input to a system running BranchCache. Successful exploitation results only in denial of service of the BranchCache service — availability impact with no information disclosure or tampering (CVSS 3.1: 7.5, AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Affected systems are Windows installations with the optional BranchCache feature enabled, such as branch-office caching deployments (Hosted Cache Servers or clients in distributed mode); the provided data does not specify affected version ranges. There is currently no known exploitation: the flaw was addressed in Microsoft's September 2026 Patch Tuesday (part of a 966-flaw release), has no public PoC, is not in CISA KEV, and carries an EPSS of 1.1% (62nd percentile).
· Microsoft Windows BranchCache (component of Windows client and Windows Server)large
External File Path Control in Microsoft .NET Enables Network Privilege Escalation
Microsoft .NET contains a privilege elevation flaw (CWE-73) in which a file name or path processed by the .NET runtime is externally controlled, allowing an unauthorized attacker to elevate privileges over a network. Exploitation requires network access, user interaction, and a high-complexity attack path (CVSS AV:N/AC:H/PR:N/UI:R), meaning the attacker must induce a user into an action that causes .NET to process an attacker-influenced file path, though no privileges are needed. A successful attack carries high impact to confidentiality, integrity, and availability, and the associated CWEs (CWE-200, CWE-522) suggest possible information exposure and insufficiently protected credentials as related effects. Any organization running affected .NET runtimes, SDKs, or .NET Framework installations is potentially exposed; exact version ranges are not specified in the available data, and fixes shipped as part of Microsoft's September 2026 Patch Tuesday (September 8, 2026). There are no known reports of exploitation, no public proof-of-concept, the flaw is absent from CISA's KEV catalog, and EPSS assigns only a 0.5% probability of exploitation within 30 days (42nd percentile).
Use-After-Free in Windows Cloud Files Mini Filter Driver: Local Privilege Escalation
CVE-2026-80093 is a use-after-free memory-safety flaw (CWE-416) in the Windows Cloud Files Mini Filter Driver (cldflt.sys), the in-box kernel filesystem filter that backs cloud placeholder files via the Cloud Files API. An attacker who already holds valid low-privilege credentials on a host triggers the flaw through specific operations against cloud-files placeholders, causing the driver to reference freed kernel memory; the High attack-complexity rating indicates the required conditions do not line up trivially. A successful exploit elevates the attacker's privileges locally, granting full control of the affected machine with high impact to confidentiality, integrity, and availability — the flaw is not remotely exploitable on its own. Virtually every maintained Windows 10/11 and Windows Server deployment ships this driver, so any Windows host where untrusted users can run code is plausibly affected; the available data does not list specific affected builds, and fixes shipped in Microsoft's September 2026 Patch Tuesday. As of the data available there is no public PoC, the CVE is not in CISA KEV, and EPSS is low (0.3%, 28th percentile), indicating no confirmed exploitation in the wild; while the September 2026 release included two zero-days, whether this CVE is among them is not confirmed here.
· Microsoft Windows (Cloud Files Mini Filter Driver, cldflt.sys) PoC mass
Use-After-Free Local Privilege Escalation in Microsoft Windows AVCTP Component
CVE-2026-69401 is a use-after-free (CWE-416) in the Audio Video Control Transport Protocol (AVCTP) component of Microsoft Windows, the protocol layer used to control Bluetooth audio and video devices. A local, authorized (low-privileged) attacker can trigger the flaw by interacting with the vulnerable protocol handling such that memory is freed while still in use, though the high attack-complexity score indicates reliable triggering is non-trivial. Successful exploitation lets the attacker elevate privileges locally on the affected machine, with high impact to confidentiality, integrity, and availability once elevated. Any Windows system that includes the AVCTP/Bluetooth component is affected, meaning a very broad portion of the Windows installed base. Exploitation status is currently calm: there is no known public proof-of-concept, the flaw is not in CISA KEV, EPSS is low at 0.2%, and the fix shipped as part of Microsoft's September 2026 Patch Tuesday (966 flaws fixed, including 2 zero-days).
· Microsoft Windows (Audio Video Control Transport Protocol / Bluetooth AVCTP component)mass
Unauthenticated DoS in Microsoft Active Directory Federation Services (AD FS)
CVE-2026-72978 is an unauthenticated denial-of-service flaw in Microsoft Active Directory Federation Services (AD FS) caused by allocation of resources without limits or throttling (CWE-770). An attacker triggers it by sending network requests that cause the AD FS service to allocate resources without bound, exhausting capacity; the high attack-complexity score (AC:H) indicates the exhaustion condition is not reliably achieved on every attempt. A successful attack yields availability impact only (A:H) — the federation service can be knocked offline, interrupting sign-in/SSO for users who depend on it, with no confidentiality or integrity impact. Organizations running AD FS — typically enterprises using federated authentication with Microsoft 365/Entra ID on Windows Server — are affected. There is currently no evidence of exploitation (not in CISA KEV, no public PoC), EPSS puts the 30-day exploitation probability at 0.8%, and the fix shipped in Microsoft's September 2026 Patch Tuesday, which resolved 966 flaws including 2 zero-days.
· Microsoft Active Directory Federation Services (AD FS)large
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