A new phishing kit abuses a legitimate Microsoft device authorization flow to steal authentication tokens, register attacker-controlled devices and gain persistent access to a victim’s Microsoft 365 environments.
Microsoft 365 users are being tricked into handing over access to their accounts by a new phishing kit, GhostCode, that exploits a weakness in a legitimate device authorization flow. Researchers in eSentire’s threat response unit identified the campaign in late August 2026.
The kit abuses Microsoft’s OAuth 2.0 device authorization grant flow, a legitimate mechanism designed to enable authentication from IoT devices, smart TVs, printers, or other devices that cannot easily support a conventional browser-based login. The technique, known as device-code phishing, has been seen in other attacks before. As part of the flow, the device displays a code for the user to enters in a browser on another device to complete authentication.
GhostCode poses as one such device, gets Microsoft’s OAuth to generate a device code and then convinces the victim to enter it on Microsoft’s authentication page. The victim then signs in and completes multifactor authentication as normal — but the authentication is for the attacker-controlled device, allowing them to obtain the resulting authentication tokens. These tokens are then used to register attacker-controlled devices, obtain additional credentials and establish persistence in the victim’s Microsoft environment.
In the campaign observed by eSentire, the attack involved a social-engineering setup where attackers pose as procurement officers through a web contact form before moving conversations to an NDA-themed HTML file. Opening the file took the victim to the device-code phishing page.
Stolen tokens allow persistence
GhostCode’s post-authentication activity is focused on turning the stolen access into persistence inside the Microsoft environment. Once access was granted, eSentire recorded nine successful API calls over a 78-second period, involving Microsoft Intune Enrollment, the Device Registration Service, Azure Active Directory and Microsoft Graph.
Three devices were registered during that time, at 28, 53 and 77 seconds after authentication, a sequence eSentire said was automated.
The third device was also successfully enrolled into Intune, Microsoft’s cloud-based device management service. eSentire noted that Intune enrollment survived token revocation: The attacker-created device remained in the tenant until it iwas explicitly removed.
The attackers also obtained a Primary Refresh Token (PRT), which eSentire called “one of the most powerful” credentials in a Microsoft identity environment.
“Obtaining a PRT via device code abuse gives the threat actors essentially SSO-equivalent access to the victim’s entire M365 environment for the PRT’s lifetime — including any service not explicitly protected by a Conditional Access policy requiring a compliant device,” eSentire said, adding that the token persists 14 days by default.
The attackers also employed multiple evasion techniques, including padding and obfuscating the HTML code in their lure, encrypting redirects, checking for bots, and using Cloudflare Turnstile to keep security tools away from the phishing page.
What defenders can do
To defend against attacks like this, eSentire’s researchers recommend restricting Microsoft’s device-code authentication flow through Conditional Access and disabling it for users who do not need it. It also
They also advise monitoring the Device Registration Service for multiple device registrations from a single non-interactive session, and looking for activity involving the user agent python-requests following device-code authentication.
Auditing Entra ID for devices matching GhostCode’s naming pattern and correlating successful device-code authentication with subsequent Python-based requests, should be able to catch an attack in progress, the company said. It shared a list of indicators of comprise related to the campaign to aid detection.
GhostCode adds to a growing number of attacks abusing device-code phishing to target Microsoft’s OAuth authentication flow. Recent examples include attacks using the “EvilTokens” phishing-as-a-service (PhaaS) kit, a campaign reported by KnowBe4 in February 2026, and activity observed in December 2026 involving multiple clusters, including both financially motivated and state-sponsored actors.
This article first appeared on Computerworld.