# Head Mare APT Exploits Unpatched TrueConf Server Flaws to Deploy PhantomCore and PhantomGraph Backdoors

> Kaspersky (Securelist) reports that in July 2026 the Head Mare group, recently reclassified from hacktivist to APT, chained two unauthenticated vulnerabilities (KLCERT-26-057, KLCERT-26-058) in unpatched TrueConf Server (5.3.X-5.3.9, 5.4.X-5.4.9, 5.5.X-5.5.5) to gain NT AUTHORITY\SYSTEM access, plant a PHP web shell, trojanize the TrueConf Client installer with the PhantomCore backdoor, and deploy the dual-module PhantomGraph backdoor (SysExcSvc.dll/SysReadSvc.dll) against Russian instrument-manufacturing, electronics, transportation, energy, IT, and software-development organizations.

- **Published:** 2026-08-11T00:00:00Z
- **Last reviewed:** 2026-08-11T00:00:00Z
- **Canonical:** https://intel.threadlinqs.com/threat/TL-2026-1982
- **ID:** TL-2026-1982
- **Severity:** CRITICAL
- **Category:** APT
- **Status:** ACTIVE
- **Actor:** Head Mare
- **Detections:** 9 · **IOCs:** 28 (full data via the Threadlinqs MCP server — Purple tier)

## Description

In July 2026, Kaspersky's Securelist detected in-the-wild exploitation of two vulnerabilities in TrueConf Server, an on-premises video-conferencing platform, by the Head Mare group -- a cluster Kaspersky has now reclassified from hacktivist to advanced persistent threat based on the sophistication of its tradecraft. The attack chain began with an unauthenticated connection to TCP/4307, open by default on vulnerable TrueConf Server builds (versions 5.3.X through 5.3.9, 5.4.X through 5.4.9, and 5.5.X through 5.5.5). KLCERT-26-057 allowed the attacker to transmit and execute a malicious script inside TrueConf's isolated execution environment; KLCERT-26-058 then let that script escape the sandbox and run arbitrary OS-level commands, escalating to NT AUTHORITY\SYSTEM. TrueConf shipped patches for both flaws on June 18, 2026 (5.3.9, 5.4.9, 5.5.5), but the attacks Kaspersky observed occurred against servers that had not applied them.

With SYSTEM-level access, the operators replaced '...\public\js\locale.php' with a PHP web shell (MD5 4d27b4eb1c5dbb3d8160f29b8119523e) for persistent remote access, then used that access to enumerate the server's infrastructure, escalate privileges inside the TrueConf database, and replace the legitimate TrueConf Client installer with a trojanized build carrying the PhantomCore backdoor. Because the malicious installer lacks TrueConf's valid code-signing signature, organizations that update their clients from a compromised server -- including third-party or partner TrueConf servers -- are exposed even if their own infrastructure is patched, turning the compromise into a software-supply-chain-style distribution vector. PhantomCore is a Windows backdoor that persists via a COM-hijacking registry key under HKEY_CURRENT_USER\Software\Classes\CLSID\{0340F119-A598-4ed9-B0AC-6F6A12D3E755}\InprocServer32.

Alongside PhantomCore, the operators deployed PhantomGraph, a modular Windows backdoor split across two DLLs -- SysExcSvc.dll (receives operator commands and returns results) and SysReadSvc.dll (executes the commands, largely via dropped batch files) -- installed as Windows services (SysExcSvc/SysReadSvc) through Base64-encoded PowerShell one-liners, and staged under C:\Windows\System32\inetsrv\. PhantomGraph's command-and-control channel rides Microsoft OneDrive cloud-storage accounts rather than a dedicated C2 server, and the operators separately established SSH reverse tunnels for interactive access. Post-exploitation activity included dumping LSASS process memory for credential theft and basic host/user reconnaissance (hostname, whoami). Kaspersky's telemetry also ties the intrusion set to Linux ELF backdoors and a rootkit, indicating a cross-platform toolkit rather than a Windows-only operation.

Head Mare has targeted TrueConf infrastructure before: per The Hacker News, the group exploited a separate set of TrueConf vulnerabilities (BDU:2025-10114, BDU:2025-10115, BDU-2025-10116) to deliver PHP web shells beginning around September 2025, with that campaign publicly disclosed in April 2026. Targeting in the current campaign is confined to Russian organizations across instrument manufacturing, electronics, transportation, energy, IT, and software development -- sectors consistent with espionage-oriented rather than financially or ideologically motivated intrusion activity, notwithstanding the group's hacktivist origin.

## MITRE ATT&CK

- T1190 Exploit Public-Facing Application
- T1195.002 Compromise Software Supply Chain
- T1059.001 PowerShell
- T1059.003 Windows Command Shell
- T1569.002 Service Execution
- T1546.015 Component Object Model Hijacking
- T1543.003 Windows Service
- T1140 Deobfuscate/Decode Files or Information
- T1036.005 Match Legitimate Resource Name or Location
- T1003.001 LSASS Memory
- T1033 System Owner/User Discovery
- T1082 System Information Discovery
- T1071.001 Web Protocols
- T1102.002 Bidirectional Communication
- T1572 Protocol Tunneling
- T1020 Automated Exfiltration

## Sources

- [Head Mare APT is exploiting vulnerabilities in an unpatched TrueConf server to deliver PhantomCore and PhantomGraph to video conference participants](https://securelist.com/tr/head-mare-targets-trueconf-server-with-phantomcore/120988/)
- [Hackers breach TrueConf to trojanize client installers with backdoors](https://www.bleepingcomputer.com/news/security/hackers-breach-trueconf-to-trojanize-client-installers-with-backdoors/)
- [TrueConf Server Flaws Exploited to Replace Client Installers with PhantomCore](https://thehackernews.com/2026/08/head-mare-exploits-trueconf-flaws-to.html)
- [Hacktivist group Head Mare exploits TrueConf vulnerabilities to deliver backdoors](https://www.scworld.com/brief/hacktivist-group-head-mare-exploits-trueconf-vulnerabilities-to-deliver-backdoors)
- [Active Exploitation Alert: Head Mare Hacktivists Exploit TrueConf Vulnerabilities to Trojanize Client Installers with PhantomCore and PhantomGraph Backdoors](https://www.rescana.com/post/active-exploitation-alert-head-mare-hacktivists-exploit-trueconf-vulnerabilities-to-trojanize-client-installers-with-pha)
- [LeakWatch CW 32/2026: Metabase Zero-Day and Xbox Leak (TrueConf becomes malware gateway)](https://www.igorslab.de/en/leakwatch-cw-32-2026-metabase-zero-day-hits-framework-trueconf-becomes-malware-gateway-microsofts-xbox-plans-leak/)
- [TrueConf Server: Critical campaign with infected updates](https://www.secnews.gr/en/725958/trueconf-server-molysmeni-enimerosi/)

## Full data

Detection queries (Splunk SPL / Microsoft KQL / Sigma) and IOC values require the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp

Canonical: https://intel.threadlinqs.com/threat/TL-2026-1982