Skip to navigation

Threat reportAPTTL-2026-1982

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

criticalACTIVE

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.

Key facts for TL-2026-1982

IdentifiersTL-2026-1982
SeverityCRITICAL
Exploitation statusExploited in the wild
Affected productsTrueConf TrueConf Server
AttributionHead Mare (medium confidence)
MalwarePhantomCore
MITRE ATT&CK techniquesT1003.001 LSASS Memory, T1020 Automated Exfiltration, T1033 System Owner/User Discovery, T1036.005 Match Legitimate Resource Name or Location, T1059.001 PowerShell, T1059.003 Windows Command Shell, T1071.001 Web Protocols, T1082 System Information Discovery, T1102.002 Bidirectional Communication, T1140 Deobfuscate/Decode Files or Information, T1190 Exploit Public-Facing Application, T1195.002 Compromise Software Supply Chain and 4 more in the attack flow
MotivationESPIONAGE
Target sectorsinstrument manufacturing, electronics, transport, energy, information technology, software development
Target regionsrussia
Detection rules9 (1 shown free)
Sources7 cited sources

Detection coverage for TL-2026-1982

As of 2026-08-11, Threadlinqs Intelligence publishes 9 detection rule(s) for TL-2026-1982 across Splunk SPL, Microsoft KQL and Sigma, covering 28 indicator(s) of compromise. The whole corpus is readable without an account. Every threat comes with one complete detection in Splunk SPL, Microsoft KQL and Sigma, free for everyone; a free account adds daily TL Creds to unlock the rest. Paid plans add a larger daily allowance, correlation and the MCP server. Threadlinqs MCP server · View plans.

Free detection: TrueConf Server TCP/4307 Exploitation and locale.php Web Shell Drop (KLCERT-26-057/058)

Detects the Head Mare exploitation chain against unpatched TrueConf Server: an unauthenticated connection to TCP/4307 (open by default, used to smuggle KLCERT-26-057's sandboxed script and KLCERT-26-058's sandbox-escape) correlated with the resulting file write that replaces ...\public\js\locale.php with a PHP web shell (MD5 4d27b4eb1c5dbb3d8160f29b8119523e), giving the attacker NT AUTHORITY\SYSTEM-level persistent remote access.

  • Languages: Splunk SPL, Microsoft KQL, Sigma
  • ATT&CK: T1190, T1036.005
  • Data sources: firewall, sysmon, windows_security
  • Severity: critical
  • Confidence: high

Splunk SPL

index=network OR index=firewall dest_port=4307
| eval src_zone=if(cidrmatch("10.0.0.0/8",src_ip) OR cidrmatch("172.16.0.0/12",src_ip) OR cidrmatch("192.168.0.0/16",src_ip),"internal","external")
| join type=inner dest_ip
    [ search index=endpoint sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=11 TargetFilename="*\\public\\js\\locale.php"
      | eval dest_ip=Computer
      | table dest_ip, _time, TargetFilename, Hashes, Image ]
| where match(Hashes,"MD5=4d27b4eb1c5dbb3d8160f29b8119523e") OR TargetFilename="*locale.php"
| table _time, src_ip, dest_ip, dest_port, src_zone, TargetFilename, Hashes, Image
| sort -_time

Microsoft KQL

DeviceNetworkEvents
| where Timestamp > ago(24h)
| where RemotePort == 4307
| project Timestamp, DeviceName, LocalIP, RemoteIP, RemotePort, InitiatingProcessFileName
| join kind=inner (
    DeviceFileEvents
    | where Timestamp > ago(24h)
    | where FolderPath has @"\public\js\locale.php"
    | project Timestamp, DeviceName, FolderPath, MD5, FileName
) on DeviceName
| project Timestamp, DeviceName, RemoteIP, RemotePort, FolderPath, MD5
| where MD5 == "4d27b4eb1c5dbb3d8160f29b8119523e" or isnotempty(FolderPath)

Sigma

title: TrueConf Server Web Shell Drop via locale.php Replacement
id: a1b2c3d4-1111-4aaa-8bbb-000000000001
status: experimental
description: Detects replacement of TrueConf Server's public/js/locale.php with a PHP web shell following exploitation of the KLCERT-26-057/KLCERT-26-058 sandbox-escape chain over TCP/4307 (Head Mare / PhantomCore campaign).
references:
    - https://securelist.com/tr/head-mare-targets-trueconf-server-with-phantomcore/120988/
author: AII-Detector — ThreadLinqs Intelligence
date: 2026-08-11
tags:
    - attack.initial-access
    - attack.t1190
    - attack.defense-evasion
    - attack.t1036.005
logsource:
    category: file_event
    product: windows
detection:
    selection_path:
        TargetFilename|endswith: '\public\js\locale.php'
    selection_hash:
        Hashes|contains: '4d27b4eb1c5dbb3d8160f29b8119523e'
    condition: selection_path or selection_hash
falsepositives:
    - Legitimate TrueConf Server upgrade/patch process modifying locale.php (verify against vendor release notes and code signature)
level: critical

Known false positives:

  • Legitimate TrueConf administrative traffic on TCP/4307 from patched, trusted management hosts with no corresponding locale.php write

Tuning notes: Restrict the port-4307 leg to hosts running vulnerable TrueConf Server builds (5.3.X-5.3.8, 5.4.X-5.4.8, 5.5.X-5.5.4) and exclude the confirmed-patched fleet (5.3.9/5.4.9/5.5.5+) once remediated.

8 more detection rules (Splunk SPL, Microsoft KQL, Sigma) · unlock with TL Creds. Sign up free to unlock the detection rules or query them with the Threadlinqs MCP server (Purple)
  • Unsigned or Known-Malicious TrueConf Client Installer Execution · unlock with TL Creds
  • PhantomGraph SysExcSvc/SysReadSvc Service Installation via Base64-Encoded PowerShell · unlock with TL Creds
  • Outbound SSH Connection to Head Mare Reverse Tunnel Infrastructure · unlock with TL Creds
  • Command Execution Spawned from Web Server Process Following locale.php Web Shell Access · unlock with TL Creds
  • LSASS Memory Access and Host Reconnaissance Following PhantomGraph Service Execution · unlock with TL Creds
  • Batch Script Execution by PhantomGraph SysReadSvc with Outbound Connection to Head Mare Attack Infrastructure · unlock with TL Creds
  • PhantomCore COM Hijacking Persistence via CLSID InprocServer32 Registry Key · unlock with TL Creds
  • Anomalous OneDrive API Traffic Initiated by PhantomGraph Service Process · unlock with TL Creds

Indicators of compromise for TL-2026-1982

As of 2026-08-11, Threadlinqs Intelligence tracks 28 indicators of compromise for TL-2026-1982.

Sample indicators (3 of 28)

  • IP address: 81.177.32[.]12
  • Domain: penzadogshelter[.]site
  • File hash: 4d27b4eb1c5dbb3d8160f29b8119523e

Defanged, TLP:CLEAR. Full set of 28 indicators: unlock with TL Creds.

28 indicators of compromise · unlock with TL Creds. Compare plans

How Head Mare APT Exploits Unpatched TrueConf Server Flaws to works

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 techniques by tactic:

Credential Access

T1003.001 LSASS Memory

Exfiltration

T1020 Automated Exfiltration

Discovery

T1033 System Owner/User Discovery; T1082 System Information Discovery

Defense Evasion

T1036.005 Match Legitimate Resource Name or Location; T1140 Deobfuscate/Decode Files or Information

Execution

T1059.001 PowerShell; T1059.003 Windows Command Shell; T1569.002 Service Execution

Command and Control

T1071.001 Web Protocols; T1102.002 Bidirectional Communication; T1572 Protocol Tunneling

Initial Access

T1190 Exploit Public-Facing Application; T1195.002 Compromise Software Supply Chain

Persistence

T1543.003 Windows Service; T1546.015 Component Object Model Hijacking

Remediation for Head Mare APT Exploits Unpatched TrueConf Server Flaws to

Patches

  • TrueConf Server 5.3.9
  • TrueConf Server 5.4.9
  • TrueConf Server 5.5.5

Immediate actions

  • Apply TrueConf Server patches (5.3.9, 5.4.9, or 5.5.5, or later) immediately
  • Verify TrueConf Client installer digital signatures against the vendor's official distribution before install or update
  • Restrict or firewall inbound TCP/4307 to trusted management networks only
  • Hunt for a web shell at '...\public\js\locale.php' (MD5 4d27b4eb1c5dbb3d8160f29b8119523e) and for unsigned TrueConf installer executables

Workarounds

  • Restrict TCP/4307 to trusted management networks only if patching cannot occur immediately
  • Take unpatched TrueConf Server instances offline or isolate them from client update distribution until patched

Longer-term hardening

  • Monitor registry writes under CLSID {0340F119-A598-4ed9-B0AC-6F6A12D3E755}\InprocServer32 for COM-hijacking persistence
  • Alert on creation of the SysExcSvc/SysReadSvc Windows services and new files under C:\Windows\System32\inetsrv\
  • Detect LSASS memory access (including via comsvcs.dll) correlated with TrueConf server or client processes
  • Monitor for anomalous OneDrive API traffic used as a C2 channel and for unexpected outbound SSH reverse tunnels
  • Require code-signature verification for all software update mechanisms distributed via internal collaboration servers

Affected and fixed versions

  • TrueConf — TrueConf Server
    Vulnerable versions: 5.3.X - 5.3.8; 5.4.X - 5.4.8; 5.5.X - 5.5.4; earlier releases
    Fixed in: 5.3.9; 5.4.9; 5.5.5

Timeline of Head Mare APT Exploits Unpatched TrueConf Server Flaws to

  • Head Mare begins exploiting an earlier, separate set of TrueConf vulnerabilities (BDU:2025-10114, BDU:2025-10115, BDU-2025-10116) to deliver PHP web shells, per The Hacker News.
  • Head Mare's earlier TrueConf-targeting campaign (BDU:2025-10114/10115/10116) is publicly disclosed.
  • TrueConf releases patches for KLCERT-26-057 and KLCERT-26-058 in TrueConf Server versions 5.3.9, 5.4.9, and 5.5.5.
  • Head Mare exploits unpatched TrueConf Server instances via unauthenticated access to TCP/4307, chaining KLCERT-26-057 and KLCERT-26-058 to obtain NT AUTHORITY\SYSTEM access.
  • Operators replace '...locked-ioc-13' with a PHP web shell (MD5 locked-ioc-4) to maintain persistent remote access to the compromised TrueConf server.
  • The legitimate TrueConf Client installer is replaced with an unsigned, trojanized build carrying the PhantomCore backdoor, exposing users who update from the compromised server.
  • The dual-module PhantomGraph backdoor (SysExcSvc.dll/SysReadSvc.dll) is installed as Windows services via Base64-encoded PowerShell commands, using Microsoft OneDrive accounts for command-and-control.
  • Operators dump LSASS process memory for credential theft, perform host/user reconnaissance (hostname, whoami), and establish SSH reverse tunnels for interactive access.
  • Kaspersky Securelist publishes a detailed report on the Head Mare TrueConf campaign, including IOCs and detection guidance.

Sources cited for Head Mare APT Exploits Unpatched TrueConf Server Flaws to

More from Head Mare

Previous and next in apt

Drafted by the Threadlinqs research pipeline from 7 sources; published ; last updated —.

Threadlinqs Intelligence — Real-Time Threat Detection Platform

[ 0 threats ] [ 0 det ] [ CRIT: 0 ] [ HIGH: 0 ]
// threat_feed
$ sort --newest
Showing all threats

Live intelligence console

Threat level

Latest Threats