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:
- TerminalFix campaign deploys a reverse tunnel through multistage intrusion
August 28, 2026
Microsoft Threat Intelligence has observed a TerminalFix campaign, a variant of ClickFix, targeting organizations across multiple industries. The campaign uses compromised websites to display a fake Cloudflare CAPTCHA verification overlay that tricks users into copying and executing a malicious PowerShell command. While traditional ClickFix campaigns direct victims to the Windows Run dialog, TerminalFix campaigns apply ...
- PaperCut NG/MF Critical Zero-Day Exploited in the Wild
August 28, 2026
On August 27, 2026, PaperCut Software published an urgent security advisory stating that it is investigating active exploitation of a vulnerability affecting PaperCut NG and PaperCut MF. PaperCut has confirmed customer incidents and is treating the issue as a security emergency. At the initial time of disclosure, the vulnerability had not been assigned a CVE identifier, and ...
- Identity-as-a-Service: Uncovering Dark Web Marketplaces Trading Executive SSNs
August 27, 2026
Despite modern verification controls, identity theft remains one of the most pervasive threats to both individuals and enterprise organizations. U.S. Federal Trade Commission statistics show over 1 million identity theft reports annually, with related fraud and imposter scams accounting for billions in financial losses each year. While stolen credit cards enable rapid, short-term monetization, Social ...
- An open letter for a global surge in cyber defense
August 27, 2026
We have a limited window to strengthen cyber defenses. In the coming months, AI-enabled cyber attacks will become far more widespread and sophisticated as models around the world become increasingly capable. The companies and public services our communities depend on—from hospitals to water treatment plants to the infrastructure that powers the internet—are at risk. Today’s AI advances ...
- Millions of UK airport customer details accessed in major cyberattack
August 27, 2026
A cyber security breach targeting three major UK airports has led to the personal data of around 8.7 million customers being accessed, operator Manchester Airport Group (MAG) has confirmed. The group, which oversees Manchester Airport, London Stansted and East Midlands Airport, assured the public that “at no point has passenger safety or aviation security been compromised”, adding that no payment or banking details ...
- China-Linked Hacking Group QTFY Targets Military and Critical Infrastructure with Malicious Distributed Systems
August 26, 2026
The Federal Bureau of Investigation, National Security Agency, and Cyber National Mission Force are releasing this joint cybersecurity advisory to alert organizations concerning China-linked cyber threat actors, who use the acronyms QTFY, QT, and QTCYBER for themselves and their tools and have developed malicious distributed platforms to compromise the networks of US and foreign organizations. ...