CVE-2026-65660

CVE-2026-65660 is an improper control of code generation (CWE-94) flaw in Microsoft Office SharePoint Server that allows an authenticated, low-privilege attacker to inject and execute arbitrary code over a network. The bug is triggered after login by sending crafted input that SharePoint processes and executes, so any account with basic access to the SharePoint site — including a standard user — is a viable attack path. Successful exploitation yields remote code execution on the SharePoint server with the privileges of the SharePoint service account, threatening full compromise of confidentiality, integrity, and availability (CVSS 8.8). Notably, Microsoft initially classified the flaw as spoofing before it was recharacterized as authenticated RCE, and Canada's Cyber Centre has issued advisory AL26-023 about it. A public proof-of-concept exists on GitHub, but the issue is not in CISA's KEV catalog and there are no confirmed reports of in-the-wild exploitation yet, though EPSS (1.2%, 67th percentile) suggests above-average likelihood of attempted exploitation.

What to do: Apply Microsoft's security update for SharePoint Server from the corresponding Patch Tuesday release as soon as possible, prioritizing any server reachable from the internet or exposed to broad internal user populations. Because exploitation only requires an authenticated low-privilege account, review recent SharePoint audit logs for anomalous behavior by ordinary users (unexpected page/app modifications, unusual requests preceding process activity), and enforce least-privilege access so standard accounts cannot reach sensitive site collections. Verify patch levels across all SharePoint farms, including pre-production and forgotten servers, and monitor Microsoft's advisory and the Canadian Cyber Centre's AL26-023 for updates on active exploitation.