SharePoint: zero-day EoP

It’s a rare Patch Tuesday which doesn’t include multiple SharePoint fixes, and today is no exception. Microsoft is aware of existing in-the-wild exploitation of CVE-2026-56164, where successful exploitation allows an attacker to elevate privileges over a network, with no existing privileges required, and low attack complexity since “an attacker does not require significant prior knowledge of the system, and can achieve repeatable success”. This is as good an example as any that a relatively low CVSS v3 base score (5. 3) may be an imperfect signal concealing something much spicier, and Microsoft acknowledges that possibility by assigning a severity rating of Important. Microsoft certainly intended to list CVE-2026-56164 in the new Notable CVEs section of the Security Update Guide instead of erroneously listing CVE-2026-56155 twice, and it’s likely that this will be corrected shortly.