September 2026 Patch Tuesday forecast: All we need is more time

Microsoft SharePoint Server is affected by a weak authentication vulnerability (CWE-1390) that allows an unauthorized attacker to bypass a security feature over a network. Per the CVSS vector, exploitation requires no privileges and no user interaction with low attack complexity, so any unauthenticated attacker with network access to a vulnerable server can trigger it remotely. Impact to confidentiality and integrity is rated high (CVSS 9.1, critical), meaning the bypass effectively grants the attacker access that authentication should have prevented, with no direct availability impact. All organizations running on-premises Microsoft SharePoint Server are potentially affected; the source data does not specify affected version ranges or fixed builds, so defenders should consult Microsoft's advisory for those details. The flaw is under active exploitation: a public proof-of-concept is available on GitHub, attackers began exploiting it after the PoC went public, and CISA added it to the Known Exploited Vulnerabilities catalog on 2026-08-18 (EPSS ~40%, 99th percentile; ransomware association unknown).

Do: Apply Microsoft's security update for CVE-2026-55040 immediately, prioritizing internet-facing SharePoint servers, and comply with CISA BOD 26-04 and the agency's Forensics Triage Requirements, including checking for signs of prior compromise on SharePoint servers. Use the public GitHub proof-of-concept to validate patching and detection coverage, and restrict network exposure of SharePoint until all servers are updated.

Microsoft Exchange Server contains an authentication bypass flaw (CWE-294) in which captured authentication material can be replayed, allowing an authorized attacker to elevate privileges over a network. Per the CVSS vector, the attack is network-based with low complexity but requires the attacker to already hold low privileges and some user interaction, and success yields high impact on confidentiality, integrity, and availability. Affected products include on-premises Exchange Server and Exchange Server Subscription Edition, though specific vulnerable version ranges are not specified in the available data. Public scans indicate nearly 22,000 Exchange servers remain exposed to the flaw following the August 2026 Patch Tuesday fixes. No in-the-wild exploitation, public proof-of-concept, or KEV listing is known; the bug was demonstrated at Pwn2Own (ZDI-26-534) and carries an EPSS estimate of 1.3% probability of exploitation within 30 days.

Do: Apply the Exchange Server security updates released in Microsoft's August 2026 Patch Tuesday (refer to Microsoft's advisory for the exact fixed builds) on all on-premises servers, prioritizing internet-facing systems running OWA, EWS, or ActiveSync. Until patched, limit network exposure of Exchange endpoints to trusted networks and monitor authentication logs for replay-style anomalies; per the scan data, roughly 22,000 servers still need the update.

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).

Do: Apply Microsoft's Patch Tuesday security updates for SharePoint Server as soon as possible, prioritizing internet-facing farms, since the flaw requires no authentication and grants code execution. As interim mitigation, restrict network exposure of SharePoint front-ends (VPN/WAF/reverse proxy rules) and verify all farm servers receive the update. Monitor vendor advisories and the Rapid7 analysis for details on the vulnerable code paths, since no public PoC or in-the-wild exploitation has been confirmed yet.

CVE-2026-65801 is a server-side request forgery (CWE-918) in Microsoft's cloud-hosted Exchange Online service that an unauthorized attacker can reach over the network without credentials or user interaction. A crafted request causes Exchange Online server components to issue requests toward internal service endpoints, and the scope-changed CVSS 3.1 vector (S:C with high confidentiality, integrity, and availability impact) indicates the resulting privilege elevation extends beyond the initially targeted component. A successful attacker gains elevated privileges within the Exchange Online service, potentially enabling broader access to mailbox data and service functionality. All organizations with mailboxes hosted in Exchange Online are in scope; because this is a flaw in Microsoft's managed service, customers cannot patch it themselves and depend on Microsoft's service-side remediation. Exploitation has not been publicly confirmed: the flaw is not in CISA KEV, no public proof-of-concept is known, and EPSS estimates only about a 0.5% probability of exploitation within 30 days.

Do: Monitor the MSRC advisory for CVE-2026-65801 and the Microsoft 365 admin center Message Center for Microsoft's service-side fix and remediation timeline; no customer-side patch or version upgrade applies. Until remediation is confirmed, review Exchange Online audit logs (Unified Audit Log) for anomalous privilege changes or unusual server-side activity, and report any suspected exploitation to MSRC.

Microsoft Azure Arc contains a use of incorrectly-resolved name or reference (CWE-706) that allows an unauthorized, unauthenticated attacker to elevate privileges over a network. The flaw is triggered through network access alone, with no privileges, user interaction, or complex conditions required, as reflected in its maximum CVSS 3.1 score of 10.0 (AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H). The scope-changed metric indicates the attack crosses a security boundary, so an attacker who reaches the vulnerable component could gain elevated privileges with high impact on confidentiality, integrity, and availability. Organizations that have enrolled on-premises or multicloud resources into Azure Arc are affected; the source data provides no specific affected version ranges, and the CPE product entry also references Azure Web Apps while the description names Azure Arc. There is currently no known public proof-of-concept, the issue is not in CISA KEV, and EPSS assigns a 0.5% 30-day exploitation probability (43rd percentile), indicating no confirmed in-the-wild exploitation.

Do: No fixed version numbers are included in the source data, so consult Microsoft's advisory and the September 2026 Patch Tuesday release for the Azure Arc update and apply it promptly when published. In the meantime, inventory Azure Arc-enabled servers and other enrolled resources, restrict network exposure of Arc agent and management endpoints to trusted management paths, and monitor Microsoft's advisory for changes to exploitation status. Given the maximum CVSS score but no PoC or KEV listing yet, treat this as a high-priority patch rather than an emergency, and escalate if Microsoft confirms active exploitation.

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.

Do: Ensure Microsoft Defender and its Malware Protection Engine are fully up to date by installing the latest antimalware platform and security intelligence (definition) updates via Windows Update, WSUS/SCCM/Intune, or Defender for Endpoint, and verify the installed engine version against Microsoft's advisory since PoC reports claim the initial patch can be bypassed. Given the local, low-privilege attack path, prioritize hosts where untrusted users or code run locally, such as shared servers, RDS/terminal hosts, and developer workstations. Monitor Microsoft and researcher channels for follow-up engine updates or revised guidance addressing the reported patch bypass.

Microsoft Azure Arc, the service used to manage on-premises and multi-cloud servers from Azure, contains an incorrect authorization flaw (CWE-863) in which permission checks fail to properly restrict what an unauthorized party may do. Per the CVSS vector, the flaw is exploitable over a network with no privileges or user interaction required, and exploitation changes the security scope, allowing an unauthorized attacker to elevate privileges with high impact on confidentiality and integrity. Any organization that has enrolled servers or other resources with Azure Arc is potentially exposed. No public proof-of-concept, in-the-wild exploitation, or CISA KEV listing is known, and EPSS currently estimates only about a 0.4% probability of exploitation within 30 days.

Do: Apply Microsoft's fix as soon as it is released (expected with the September 2026 Patch Tuesday updates) and check Microsoft's advisory for affected Azure Arc components and agent versions. Until then, review and minimize permissions granted to Arc-enabled resources and restrict network reachability to Arc management endpoints. Monitor Microsoft's advisories for updated agent packages and redeploy them promptly to enrolled servers.

Google Chrome versions prior to 152.0.7977.82 contain a type confusion flaw (CWE-843) in the V8 JavaScript engine, which mishandles object types during engine operations (public proof-of-concept writeups indicate it is reachable through array sorting and WebAssembly-related code paths). A remote attacker triggers the flaw simply by getting a user to open a crafted HTML page, with no privileges or authentication required. Successful exploitation lets the attacker execute arbitrary code inside the browser's sandbox, and public reporting shows it being chained with Windows zero-days (the 'BlueMoon' exploit kit) by Chinese espionage groups for broader compromise. Any user of an unpatched Chrome or another build embedding the affected V8 engine is exposed. The vulnerability is a zero-day that was actively exploited in the wild before patching, was added to CISA's KEV on 2026-09-04, and has five public proof-of-concept references.

Do: Update Google Chrome to 152.0.7977.82 or later immediately, and apply the corresponding V8 fix in any Chromium-based browser in use. Federal agencies must apply mitigations in line with CISA BOD 26-04 and its cloud-services requirements, evaluating each asset's internet exposure. Because public reporting shows this flaw chained with Windows zero-days in 'BlueMoon' attacks, patch the related Windows vulnerabilities as well and hunt for signs of exploit-chain activity on high-exposure endpoints.