漏洞描述
Microsoft SharePoint Server (2016, 2019, Subscription Edition <= 2026.3.1) contains a remote code execution vulnerability in the WS-Federation passive sign-in endpoint (/_trust/default.aspx). The SharePoint authentication module (SPFederationAuthenticationModuleV2) uses a deflate-only DeflateCookieTransform (no MAC/signature check) to decode and BinaryFormatter to deserialize the SecurityContextToken Cookie value in the wresult parameter without type restrictions. An unauthenticated attacker can send a crafted WS-Federation token containing a BinaryFormatter gadget chain (DataSet + LosFormatter + XamlAssemblyLoadFromFile) to execute arbitrary code in the context of the IIS application pool identity (w3wp.exe). The fix (KB5002882, July 2026 CU) replaces the DeflateCookieTransform with NotSupportedCookieTransform, making ReadToken() throw before deserialization.
影响产品
修复建议
建议关注厂商安全公告，及时升级至已修复版本，并结合实际资产暴露情况采取缓解措施。