RCE via path traversal in Microsoft SharePoint Upload.aspx
CVE-2026-45454 is a path traversal flaw in Microsoft SharePoint Server's file upload page, /_layouts/15/Upload.aspx. The vulnerable code path uses UploadPage.CurrentFolder to resolve the upload destination from the user-controlled RootFolder query string parameter and fails to verify that the resolved folder belongs to the document library identified by the List parameter. As a result, an authenticated user with upload rights to one document library can cause SharePoint to write files into a different library on the same site. The upload operation ultimately reaches SPFolder.Files.Add() after RootFolder is read from the HTTP request via SPRequestParameterUtility.GetValue and resolved through PrivateWeb.GetFolder(). In environments where the target path is the Master Page Gallery (/_catalogs/masterpage) and SharePoint PageParserPaths is configured to allow server-side script execution there, the arbitrary file upload can be escalated to remote code execution by uploading an ASPX webshell. Microsoft fixed the issue by adding a ParentListId ownership check and null-list validation in microsoft.office.policy.pages.dll.
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