Microsoft SharePoint Server unauthenticated elevation of privilege (exploited zero-day)

Microsoft July 2026 Patch Tuesday ships two actively-exploited zero-days — AD FS local EoP (CVE-2026-56155) and unauthenticated SharePoint EoP (CVE-2026-56164)

Microsoft's July 2026 Patch Tuesday is its largest ever by CVE count and carries two zero-days Microsoft confirms were exploited before a fix existed, both added to CISA's Known Exploited Vulnerabilities catalog the same day (BleepingComputer, 2026-07-14). CVE-2026-56155 (CVSS 7.8, CWE-1220) is a local elevation-of-privilege in Active Directory Federation Services: an attacker who already holds a low-privileged authorized session on the AD FS host escalates to administrator (Microsoft MSRC, 2026-07-14). It is a post-foothold escalation rather than an initial-access vector, and Microsoft's advisory credits its own DART incident-response team in the acknowledgements — meaning it surfaced during a live intrusion, so an exposed AD FS host should be treated as a candidate for compromise assessment, not merely patched (Microsoft MSRC, 2026-07-14). CVE-2026-56164 (CVSS 5.3, CWE-306) is the more exposed of the two: a missing-authentication flaw in on-prem SharePoint Server that lets an unauthenticated attacker elevate privileges over the network with no user interaction (Microsoft MSRC, 2026-07-14). Microsoft's mitigation guidance — enable AMSI on the SharePoint/IIS worker processes with Request Body Scan set to Full — indicates the trigger is a crafted HTTP POST body, the same class of exposure this pipeline tracked for the CVE-2026-45659 SharePoint deserialization RCE on 2026-07-02, so operators who already tuned AMSI for that flaw have partial coverage.