Microsoft warned that extortion groups including ShinyHunters are running passkey and single-sign-on-themed phishing to break into Microsoft 365 accounts. Attackers impersonate the IT help desk by call, text, or Teams message, urging employees to urgently update a passkey or MFA setting, then send them to fake login pages. The passkey angle is only a lure: the real goal is to capture credentials and session tokens through an adversary-in-the-middle site or a device-code approval that bypasses MFA. Once in, they register their own authentication method for persistence, so a password reset alone will not evict them, then quietly exfiltrate under a thousand files an hour to blend in, spreading through connected single-sign-on services.
Researchers describe attackers using voice phishing calls to talk employees into granting access from their personal devices, then reaching Microsoft 365 and corporate data through the trust the user extends. The attackers do not hack the device; they convince the person, then use Microsoft's Graph API to identify valuable targets and pass access to extortion groups like ShinyHunters. Because the weakness is the user's decision rather than the hardware, banning personal devices would not stop it. The stronger defense is tightening identity and authentication and limiting what a compromised account can actually do, so that tricking one person yields far less to the attacker.
Researchers at CloudSEK gained access to the control panel of BigBear, a phishing-as-a-service platform that defeated multi-factor authentication at 258 organizations and stole thousands of Microsoft 365 credentials. It uses an adversary-in-the-middle proxy based on Evilginx to sit between victims and Microsoft's real login, capturing passwords, multi-factor codes, and the session cookie, then replaying the cookie to hijack the already-authenticated session. The panel logged over 5,000 stolen records across 40-plus countries and is rented to multiple affiliates who receive stolen data through Telegram bots. Notably, it runs JavaScript that disables the browser's passkey support, forcing victims off phishing-resistant login onto weaker methods it can intercept.
The extortion group ShinyHunters published data stolen from Questel, a French intellectual-property software and services firm, after a voice phishing call gave attackers access to a Sales SharePoint site in its Microsoft 365 environment. The group claimed more than 21 million records, but the published corpus verified out to about 1.2 million real email addresses, along with names, employers, job titles, physical addresses, and phone numbers, mostly corporate contacts from sales and marketing. Questel confirmed the unauthorized access but has not endorsed the larger figure. It is the same voice-phishing-into-connected-cloud pattern, and the same inflated-claim behavior, seen in other recent ShinyHunters cases.
A commercial phishing-as-a-service toolkit called Mirage2FA has hit around 4,500 organizations by abusing legitimate Microsoft 365 login flows to steal passwords and session cookies and bypass two-factor authentication. Because it captures the session cookie after a real login completes, the attacker inherits an authenticated Microsoft 365 session and any single-sign-on connected services, defeating multi-factor authentication. Researchers at ANY.RUN linked the campaign to more than 9,000 potential compromise events and found that nearly half of targeted addresses may have been affected, with most victims in the United States across technology, manufacturing, and education. Hijacking one session can expand into connected apps and internal workflows.
A researcher disclosed a prompt-injection technique that turns Microsoft 365 Copilot for Word into a carrier for self-spreading instructions. Malicious commands hidden as tiny white-on-white text in a document are invisible to a reader but read in full by Copilot when the file enters its context during a drafting or editing task. Copilot then follows them, in one example silently altering financial figures in a report, and copies the same hidden instructions into the new document, which becomes a fresh carrier for the next person who uses it. It does not spread on its own, but Microsoft's mitigations over 144 days blocked specific wordings without fixing the underlying class.
Volexity has detailed Chinese espionage group UNC5221 (also VerdantBamboo) maintaining access to a victim's Microsoft 365 environment using the Brickstorm backdoor plus previously undocumented malware named Plenet and AgentPSD. The actor sat on the network at least 18 months before detection and had also compromised the victim's MSP. UNC5221 has exploited edge-device zero-days since at least 2023; Brickstorm began as Golang, later Rust. In this case the group pivoted from a compromised Egnyte Storage Sync system through the victim's SSL VPN, then used Brickstorm proxying and stolen credentials to reach Microsoft 365 - deliberately blending with legitimate traffic to evade Conditional Access. It re-breached the org after remediation.
Researchers have detailed a cyber-espionage campaign in which attackers maintained access to a global stock exchange executive's Microsoft Outlook mailbox for roughly five months. The intrusion relied on a malicious OAuth application and inbox-rule persistence to quietly read and forward mail while evading detection. By abusing OAuth consent rather than stealing a password, the attackers retained access that survived password changes and looked like routine application traffic in logs. The five-month dwell time on a single high-value executive points to a patient, intelligence-driven operation rather than opportunistic crime. The case reinforces the now-recurring pattern of OAuth-app abuse and malicious inbox rules as the core of stealthy Microsoft 365 mailbox compromise.
Enclave researchers have disclosed FlagLeft, a flaw in Microsoft 365 Android apps that let any local app steal account tokens because a shared Microsoft SDK shipped with setIsDebugMode(true) left in production code, skipping the check that should reject untrusted apps requesting SSO handoff. The leaked FOCI single-sign-on tokens can be refreshed and reused over long periods, with traffic that looks routine in logs. It affected Word, PowerPoint, Excel, Microsoft 365 Copilot, Loop, and OneNote (billions of downloads); Teams shipped the flag false and was unaffected. Microsoft issued four CVEs on May 12 (CVE-2026-41100/41101/41102/42832). The patched Android Word build is 16.0.19822.20190; a malicious on-device app is all it takes.
Dark Reading reports that Kali365 - the phishing-as-a-service platform the FBI flagged for fueling Microsoft 365 attacks in April - is expanding its reach. Rather than stealing passwords, Kali365 captures OAuth access and refresh tokens by tricking victims into completing attacker-initiated Microsoft device-login requests, granting immediate mailbox access. The service generates branded lures impersonating Adobe, DocuSign, and SharePoint in many languages and sells in tiers from $250 for 30 days to $2,000 annually. Its continued growth signals that OAuth device-code consent phishing remains a high-yield technique, and that defenders should prioritize blocking device-code flows for non-mobile platforms and enforcing phishing-resistant MFA across Microsoft 365 tenants.
TrustStrike Labs