View Ridge Security
Back to Cyber Hose

HollowGraph Malware Uses Microsoft 365 Calendar for Stealthy C2

HollowGraph malware abuses Microsoft 365 calendar events for command and control, targeting organizations in Israel.

🕵️ RESEARCH & DEEP DIVES

  • HollowGraph malware uses Microsoft 365 calendar for stealthy C2 communications — BleepingComputer
    HollowGraph malware abuses Microsoft 365 calendar events to receive commands and exfiltrate data, targeting organizations in Israel.

    • Targets Microsoft 365 mailboxes, focusing on organizations in Israel
    • Uses Microsoft Graph API with hardcoded credentials to access mailbox calendar
    • Commands and stolen data hidden in calendar events dated May 13, 2050
    • Employs hybrid RSA and AES-256-GCM encryption for secure C2 communication
    • Uses DNS tunneling via IPv6 AAAA queries to update Microsoft Entra ID credentials
  • Authenticated RCE in EGroupware via Malicious eTemplate Upload (CVE-2026-40187) — CVE ThreatInt
    Authenticated administrators can execute OS commands on EGroupware servers by uploading malicious eTemplate XML files.

    • Applies to EGroupware versions 26.0 and earlier
    • Vulnerability allows OS-level Remote Code Execution (RCE)
    • Exploited by uploading a malicious eTemplate XML file (.xet) to the /etemplates VFS mount
    • Attack leverages PHP eval() call with unescaped backtick characters to execute shell commands
    • Requires authenticated administrator privileges to exploit
  • Exposed Server Reveals AI-Assisted Phishing Toolkit Targeting Windows via WebDAV — The Hacker News
    An AI-assisted phishing toolkit delivers infostealers via WebDAV shares to Windows users, primarily in Mexico.

    • Targets Windows users, primarily in Mexico, via fake government ID lookup sites
    • Delivers infostealer malware through WebDAV shares using .scr executables disguised as PDFs
    • Exploits WebDAV working-directory hijack vulnerability (CVE-2025-33053) and tests 59 signed binaries for hijack
    • Operator used generative AI tools to develop, test, and document phishing delivery methods
    • Campaign logged 77,098 requests over 5.5 days with 96.9% launch activity from Mexico
  • Attackers Use 'TFF Trap' Fileless Loader to Deploy RATs in BEC Phishing Campaigns — Dark Reading
    Attackers use fileless loaders in business email compromise phishing campaigns to deploy multiple remote access trojans and stealers.

    • Targets include victims of business email compromise (BEC) phishing campaigns
    • Delivers remote access trojans (RATs) and stealers like Agent Tesla, Remcos, XWorm, Best Private Logger
    • Uses fileless techniques and loaders with low detection rates to evade security tools

🔓 CVEs & KEV

  • 19 CVEs reported with the worst scoring 8.0 — Various sources

Need help assessing your exposure?

Start with the free Posture Self-Check to see where you stand against the current threat landscape.

Free Posture Self-Check