security
Malware hides commands in appointments set for 2050 and uses Redmond's own cloud to phone home
Microsoft 365 calendars have become the latest hiding place for espionage malware, with attackers stashing commands and stolen files inside appointments dated 24 years into the future.Researchers at Group-IB say they've uncovered a malware component they call HOLLOWGRAPH that swaps the usual command-and-control server for something rather less conspicuous – a compromised Microsoft 365 calendar. Instead of reaching out to attacker-controlled infrastructure for instructions, the implant rummages through calendar events, picks up encrypted tasking, and drops stolen files into new appointments for its operators to collect later.
Every event created by HOLLOWGRAPH is dated May 13, 2050, an otherwise empty corner of the diary where encrypted attachments are less likely to attract attention. HOLLOWGRAPH isn't exploiting Microsoft Graph so much as blending into it, wrapping its command-and-control traffic inside legitimate Graph API requests that look just like any other Microsoft 365 application talking to the cloud.
The malware itself is relatively lean. Group-IB says it does little more than fetch instructions from one calendar event, stash stolen files in another, and periodically retrieve fresh Entra ID credentials over a DNS tunneling channel so the Graph-based communications keep working.The security firm linked the malware to the Cavern framework with high confidence after finding matching command formats and other implementation details. It also spotted similarities with the Iranian-linked espionage group Lyceum, although it stopped well short of pinning the operation on that crew, saying the connection was supported with only low confidence.
