Microsoft sounds alarm as perfect-10 Entra ID flaw comes under attack

Microsoft has fixed a maximum-severity vulnerability in Entra ID that attackers were already exploiting in the wild. Tracked as CVE-2026-69836, the vulnerability carries the maximum CVSS score of 10.0 and could allow an unauthenticated attacker to execute code remotely in Microsoft's cloud identity service. Microsoft disclosed the flaw on Thursday, along with the unwelcome news that exploitation had already been detected. Entra ID, formerly known as Azure Active Directory, sits at the heart of identity and access management for Microsoft customers, handling authentication and access to cloud applications and other corporate resources. According to Microsoft, the vulnerability stems from unsafe deserialization, in which software reconstructs data supplied from an untrusted source without adequately validating it. An attacker could exploit the weakness over a network without an account and - crucially - without persuading a user to click, open, or otherwise do anything helpful. "Deserialization of untrusted data in Microsoft Entra ID allows an unauthorized attacker to execute code over a network," Microsoft's advisory says. That is about as much as Redmond has said about the observed exploitation. The software giant hasn't disclosed who is exploiting CVE-2026-69836, when the attacks began, how widespread they are, or what attackers have done after successfully exploiting the flaw. There are also no public technical details explaining the attack chain, and Microsoft didn't immediately respond to The Register's questions. There is, however, one welcome piece of news for administrators: no customer-deployed patch is required. "This vulnerability has already been fully mitigated by Microsoft," the company said. "There is no action for users of this service to take." Because Entra ID is a Microsoft-operated cloud service, Redmond could fix the vulnerable infrastructure itself rather than ship an update for customers to install. The CVSS metrics explain the perfect 10: the flaw is remotely exploitable, has low attack complexity, requires neither privileges nor user interaction, and could have a high impact on confidentiality, integrity, and availability. Microsoft credited principal security engineer Robert Fitzpatrick with discovering and reporting the vulnerability, although the advisory does not explain how the company detected its exploitation in the wild. Microsoft may have closed the hole, but customers will still want to know who exploited it, what they reached, and how long the activity continued before Redmond shut it down. (R)