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.
The FBI has issued a warning about Kali365, a phishing-as-a-service platform that fueled large Microsoft 365 attacks in April. Instead of stealing passwords, Kali365 customers trigger Microsoft device-login requests and trick victims into completing the authorization, capturing OAuth access and refresh tokens that grant immediate mailbox access. Arctic Wolf, which infiltrated the system, says Kali365 sells in three tiers from $250 for 30 days to $2,000 for the year and generates branded phishing lures impersonating Adobe, DocuSign, and SharePoint in dozens of languages. Threat actors set malicious inbox rules to suppress security notifications and extend dwell time.
Microsoft is tracking a financially motivated actor it calls Storm-2949 that abuses the Microsoft 365 Self-Service Password Reset flow to hijack high-value identities and then exfiltrate as much data as possible. The actor socially engineers IT staff and senior leaders, kicks off an SSPR reset, then poses as IT support and convinces the victim to approve the resulting MFA prompt. Once in, Storm-2949 uses Graph API and custom Python to enumerate the tenant, downloads thousands of OneDrive and SharePoint files in single actions, and pivots into Azure - VMs, Key Vaults, SQL, storage - via privileged custom RBAC roles.
The Tycoon 2FA phishing-as-a-service kit, which Microsoft, Europol, Cloudflare and others tried to dismantle in March 2026, is back and has switched tactics. Instead of relaying credentials and MFA codes through a fake login page, operators now send victims to Microsoft's legitimate device-login page at microsoft.com/devicelogin and ask them to enter a code from the lure email. That single consent grants the attacker OAuth tokens for the victim's Exchange Online, OneDrive, and SharePoint through Microsoft's own Authentication Broker app, so it looks normal in Entra logs. eSentire spotted the late-April campaign and published IoCs, including AS45102 (Alibaba Cloud) operator infrastructure.
Push Security disclosed ConsentFix v3, a new attack that lets criminals take over Microsoft 365 accounts even if the victim has MFA and phishing-resistant passkeys turned on. The trick: instead of stealing a password, the attacker tricks the user into pasting a Microsoft authorization URL into a phishing page during what looks like a routine login. That URL contains a one-time code that the attacker exchanges for permanent access tokens. v3 automates the whole attack with Cloudflare Pages phishing sites, Pipedream webhook automation, and tenant fingerprinting that customizes the lure to each target organization's branding.
The FBI Atlanta Field Office and Indonesian authorities have dismantled the W3LL global phishing platform and arrested its alleged developer. W3LL sold a sophisticated phishing kit designed specifically for bypassing multi-factor authentication on Microsoft 365 accounts using adversary-in-the-middle (AiTM) techniques. The platform operated as a phishing-as-a-service ecosystem with its own marketplace, support channels, and licensing model, enabling thousands of business email compromise campaigns targeting corporate Microsoft 365 environments. This is described as the first coordinated international law enforcement action against this platform. Group-IB previously estimated W3LL's tools had been used to compromise over 8,000 Microsoft 365 business accounts.
TrustStrike Labs