Office 365 is Microsoft's cloud productivity suite, whose identity, email, and data controls make its vulnerabilities and security advisories consequential.
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Background for this topic.
Office 365 is Microsoft’s cloud-hosted productivity and collaboration service, encompassing Exchange Online email, SharePoint, OneDrive, Teams, and web and desktop Office applications. Because these services store communications and business documents in a shared cloud environment, the tag includes both attacks against the platform and security issues arising from tenant configuration, identity, and connected applications.
Material risks include phishing or stolen credentials leading to account takeover, malicious OAuth applications gaining delegated access, mailbox forwarding rules, and excessive external sharing of files. Effective defenses include phishing-resistant multifactor authentication, conditional-access policies, least-privilege administration, controlled app consent, data-loss prevention, and review of audit and sign-in logs. Security teams must also track Microsoft advisories and client vulnerabilities, preserve cloud evidence for investigations, and apply retention, privacy, and compliance controls appropriate to the data stored in the tenant.
Malicious actors could reduce versioning limit of files to a low number and encrypt them more times than versioning limit
A "dangerous piece of functionality" has been discovered in Microsoft 365 suite that could be potentially abused by a malicious actor to ransom files stored on SharePoint and OneDrive and launch attacks on cloud infrastructure
Security researchers are warning that threat actors could hijack Office 365 accounts to encrypt for a ransom the files stored in SharePoint and OneDrive services that companies use for cloud-based collaboration, document management and storage. [...]