The Group-IB Threat Intelligence team has identified HOLLOWGRAPH, a new malware sample that we attribute, with high confidence, to the Cavern backdoor framework. This malware is one component of a larger toolkit, and it uses the Microsoft Graph API through a compromised Microsoft 365 account observed in Israel to communicate with its operators — a technique that helps conceal command-and-control traffic within legitimate Microsoft 365 communications.
The malware supports just two commands, get and send, and executes both exclusively through trusted Microsoft cloud infrastructure. Using the Microsoft Graph API, it treats the compromised mailbox’s calendar as a two-way dead-drop: operators plant tasking as calendar events, and the implant exfiltrates stolen files by creating its own events with encrypted data attached. To avoid catching the mailbox owner’s attention, every event is dated far into the future — 13 May 2050 — with payloads attached as files to the event.
Read more…
Source: Group-IB
Sign up for the Cyber Security Review Newsletter
The latest cyber security news and insights delivered right to your inbox
Related:
- Patch these critical Fortinet sandbox bugs that let attackers bypass login, run commands over HTTP
April 15, 2026
Watch out for more Fortinet vulns! Two critical bugs in Fortinet’s sandbox could allow unauthenticated attackers to bypass authentication or execute unauthorized code on vulnerable systems. Luckily, the security vendor has issued fixes – so patch now – and so far, there are no reports of active exploitation. But considering that the vulnerabilities are now public, ...
- From fake Proton VPN sites to gaming mods, this Windows infostealer is everywhere
April 15, 2026
Malwarebytes Labs researchers uncovered multiple campaigns distributing an infostealer we track as NWHStealer, using everything from fake VPN downloads to hardware utilities and gaming mods. What makes this campaign stand out isn’t just the malware, but how widely and convincingly it’s being spread. Once installed, it can collect browser data, saved passwords, and cryptocurrency wallet information, ...
- Sweden blames Russian hackers for attempting ‘destructive’ cyberattack on thermal plant
April 15, 2026
The Swedish government said Russian government-linked hackers attempted to disrupt the operations at one of the country’s thermal power plants last year. Sweden said that, while the hackers were unsuccessful, hybrid attacks that extend beyond cyberspace are becoming more dangerous. Sweden’s minister of civil defense, Carl-Oskar Bohlin, said during a press conference on Wednesday that the ...
- Omnistealer uses the blockchain to steal everything it can
April 14, 2026
A new infostealer dubbed Omnistealer is turning the blockchain into a permanent malware hosting platform, which is bad news for both companies and everyday users. It’s pretty common for malware to store its payload on a public platform, ideally one that adds some trustworthiness to the download location, like Google docs, OneDrive, GitHub, npm, PyPI, and ...
- Patch Tuesday – April 2026
April 14, 2026
Microsoft is publishing 167 vulnerabilities on April 2026 Patch Tuesday. Microsoft is aware of exploitation in the wild for one of today’s vulnerabilities, and public disclosure for one other. Microsoft evaluates 19 of the vulnerabilities published today as more likely to see future exploitation. So far this month, Microsoft has provided patches to address 80 browser ...
- Zombie Microsoft bugs rise from the dead, pave way for crims and ransomware scum
April 13, 2026
Crooks are exploiting four Microsoft vulnerabilities – one patched 14 years ago and another tied to ransomware activity – according to America’s lead cyber-defense agency, which on Monday gave federal agencies two weeks to patch them. The four vulnerabilities added to CISA’s Known Exploited Vulnerabilities (KEV) catalog on Monday are: CVE-2025-60710, a link-following vulnerability in Windows ...