Patch Tuesday security updates for July 2026, the largest update ever. 621 CVEs in one month

Use after free in Windows VMSwitch allows an authorized attacker to elevate privileges over a network.

CVE-2026-50522 is a deserialization of untrusted data flaw (CWE-502) in Microsoft SharePoint Server that allows an unauthenticated attacker to send maliciously crafted serialized data over the network and execute code on the server, reflected in its 9.8 critical CVSS score with no privileges or user interaction required. Successful exploitation yields full remote code execution with high impact on confidentiality, integrity, and availability, giving attackers a foothold for follow-on actions such as data theft, lateral movement, or ransomware. Any organization running on-premises SharePoint Server is in scope, particularly deployments reachable from untrusted networks; the required action notes stakeholders must evaluate each asset's internet exposure under CISA BOD 26-04. The flaw is under active exploitation: CISA added it to the Known Exploited Vulnerabilities catalog on 2026-07-22 and security news headlines describe it as a critical RCE exploited in the wild, with some reports referencing exploitation after a public proof-of-concept release and an authentication bypass. The structured record lists no public PoC as confirmed, but an EPSS of 84.6% (100th percentile) underscores a very high near-term exploitation likelihood.

Do: Apply Microsoft's security updates for SharePoint Server immediately per the vendor advisory, as required under CISA's KEV listing and BOD 26-04, and prioritize any SharePoint deployments that are internet-facing (federal/critical-infrastructure operators must follow BOD 26-04 timelines or discontinue unmitigated use). Until patched, restrict public access to SharePoint endpoints (VPN, firewall rules, or reverse proxy) and review IIS/application logs and running processes for signs of unauthenticated deserialization abuse. Because some reports reference an authentication bypass being chained, also verify authentication paths and monitor for follow-on attacker activity after patching.

Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.

CVE-2026-56155 is a high-severity (CVSS 3.1: 7.8) access-control flaw (CWE-1220) in Microsoft Active Directory Federation Services (AD FS), in which insufficient granularity of access control lets an authorized attacker elevate privileges locally. Exploitation requires only low local privileges and no user interaction, so any locally authenticated user or process on a system with the AD FS role can trigger it. Successful exploitation yields full local privilege escalation with high impact on confidentiality, integrity, and availability. It affects organizations running AD FS on Windows Server 2012, 2016, 2019, 2022, and 2025, and on Windows 10 versions 1607 and 1809, per CISA's affected-products list. CISA added the flaw to the Known Exploited Vulnerabilities catalog on 2026-07-14, confirming in-the-wild exploitation despite a modest EPSS of 0.3%; it was fixed as part of Microsoft's record-breaking July 2026 Patch Tuesday.

Do: Apply Microsoft's July 2026 security updates to all affected Windows 10 and Windows Server systems, prioritizing servers hosting the AD FS role, especially federation servers tied to Microsoft 365 or hybrid identity. Per CISA KEV and BOD 26-04, federal agencies must apply vendor mitigations promptly or discontinue use, and all defenders should inventory AD FS servers, restrict local logon to them, and triage for signs of local privilege-escalation activity. No public PoC or workaround beyond patching is currently known.

Microsoft SharePoint Server contains a missing authentication for critical function vulnerability (CWE-306) that lets an unauthenticated attacker elevate privileges over a network without valid credentials. The flaw is triggered when the affected SharePoint function is accessed remotely without any authentication check, allowing an attacker to gain higher privileges than intended. Successful exploitation could enable an attacker to take elevated actions within the SharePoint environment, potentially leading to further compromise of the server and its data. All organizations running on-premises Microsoft SharePoint Server are potentially affected, though specific versions have not yet been enumerated by Microsoft or CISA. The vulnerability was added to CISA's Known Exploited Vulnerabilities catalog on 2026-07-14, indicating it is being actively exploited, and its EPSS score of 26.6% (98th percentile) reflects a high near-term exploitation risk.

Do: Apply Microsoft's security updates for SharePoint Server as soon as they are available, and check Microsoft's advisory for the specific affected version ranges once published. In the meantime, restrict network access to SharePoint servers, especially for internet-facing instances, and verify whether your environment falls under CISA BOD 26-04 requirements given the KEV listing. Monitor for updated guidance from Microsoft and CISA, as exploitation is confirmed and patching urgency is high.