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Introduction: The Quiet Danger Behind a Trusted Video Server
A video conferencing server is rarely the first system security teams expect to become the center of a sophisticated intrusion. It is usually treated as ordinary business infrastructure, something that keeps meetings running, connects employees, and quietly sits on the edge of the corporate network.
That assumption can become dangerous.
Head Mare, also known as PhantomCore, has repeatedly demonstrated how exposed collaboration infrastructure can become an entry point into targeted networks. Kaspersky has documented the group exploiting a TrueConf Server vulnerability, combining public-facing application exploitation with custom backdoors, persistence mechanisms, and post-compromise activity.
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The latest report circulating on August 11, 2026, highlights an especially concerning pattern: an attacker gains privileged access to a TrueConf environment, establishes persistence, and then uses trusted infrastructure and cloud services to move malicious components deeper into the victim environment.
The important lesson is bigger than TrueConf itself. The attack illustrates a modern reality of cybersecurity: the application that nobody considers critical can become the bridge into everything else.
What Happened in the Head Mare Campaign
According to the report shared by Cybersecurity News Everyday, Kaspersky identified Head Mare abusing unpatched TrueConf Server flaws to obtain SYSTEM-level access, deploy a web shell, and introduce PhantomCore and PhantomGraph backdoors while using OneDrive-related infrastructure for command-and-control activity.
Kaspersky’s broader research confirms that Head Mare has been actively exploiting TrueConf Server vulnerabilities, including BDU:2025-10114, in attacks against Russian organizations. The vulnerability was patched by TrueConf in August 2025, yet attackers continued finding value in systems that remained unpatched.
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This distinction matters because the most dangerous component of the attack is not necessarily an unknown zero-day.
It is the combination of known vulnerabilities, exposed services, insufficient patching, privileged execution, persistence, and carefully selected malware.
TrueConf Became the Initial Access Point
TrueConf Server is designed to provide video conferencing capabilities for organizations. Like many enterprise collaboration platforms, however, it can be exposed directly to the internet.
That makes its security posture particularly important.
Kaspersky reported that Head Mare repeatedly exploited the TrueConf vulnerability BDU:2025-10114. Researchers observed successful exploitation that allowed attackers to inject PowerShell commands through parameters associated with the TrueConf server process, ultimately enabling arbitrary code execution.
Securelist
Once a public-facing server can execute attacker-controlled commands, the security boundary around that application effectively collapses.
The attacker no longer needs to begin with a phishing email.
They can begin with the server itself.
From Application Compromise to SYSTEM Access
Obtaining application-level execution is only the beginning of an intrusion.
The real objective is usually privilege.
SYSTEM-level access on Windows gives an attacker extremely powerful capabilities. Depending on the environment, this can allow malicious processes to interact with sensitive files, services, credentials, scheduled tasks, security controls, and other components of the operating system.
This is why a vulnerability in a conferencing platform can become a much larger incident.
The vulnerability does not need to contain every capability required by the attacker.
It only needs to open the first door.
The Web Shell Changes the Game
The reported deployment of a web shell is another major warning sign.
A web shell provides attackers with a persistent or semi-persistent mechanism for executing commands remotely through a compromised web-facing service.
Instead of repeatedly exploiting the original vulnerability, an attacker can potentially return through the implanted shell.
That creates a dangerous transition:
Initial exploit → command execution → persistence → remote administration.
At that point, patching the original vulnerability alone may no longer be enough.
Security teams must investigate the compromised host for additional implants, unauthorized accounts, scheduled tasks, modified services, suspicious binaries, web shells, and outbound connections.
PhantomCore Is Not a One-Off Tool
PhantomCore is part of a broader toolkit associated with Head Mare.
Kaspersky has previously documented PhantomCore and PhantomDL in Head Mare operations, including phishing campaigns and other intrusion chains. Earlier research also showed the group using custom malware alongside tools such as Sliver, ngrok, Mimikatz, and other publicly available utilities.
Securelist
The group has continued modifying its arsenal.
Kaspersky reported PhantomHeart, for example, as a newer Head Mare backdoor that evolved from a DLL into a PowerShell implementation. The malware can communicate with command-and-control infrastructure and deploy an SSH tunnel when instructed.
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This evolution demonstrates an important pattern.
Head Mare does not appear to rely on one static malware family forever.
The infrastructure and techniques change.
The operational objective remains.
PhantomGraph Adds Another Layer of Concern
The report also references PhantomGraph alongside PhantomCore.
The significance is not simply the name of another backdoor.
Multiple implants give an attacker redundancy.
If one component is detected or removed, another mechanism may provide continued access. If one C2 channel is blocked, another may be available. If one persistence technique fails, another can take its place.
This is how relatively small pieces of malware can form a resilient intrusion framework.
The defender may see one malicious file.
The attacker sees an entire ecosystem.
OneDrive and the Abuse of Trusted Services
Using cloud infrastructure or services associated with legitimate providers creates another challenge for defenders.
OneDrive is widely used by businesses and employees. Traffic associated with Microsoft’s cloud ecosystem is therefore not automatically suspicious.
Attackers understand this.
The objective is not necessarily to make malicious traffic invisible. It is often to make it look ordinary enough to survive automated filtering and human investigation.
This is one reason modern detection cannot depend entirely on domain reputation or simple allowlists.
A trusted cloud service can still become part of a malicious communication chain.
The Attack Is Also a Supply-Chain Warning
Kaspersky previously documented a related Head Mare campaign in which compromised TrueConf servers hosted malicious versions of the TrueConf client installer. Organizations downloading those installers could potentially become infected.
Researchers reported that the attack vector used to replace the installers was unclear, although they suspected exploitation of another TrueConf vulnerability, BDU:2025-10116. The malicious installers lacked valid digital signatures.
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This is particularly disturbing because it changes the victim model.
The organization does not necessarily have to be directly targeted.
It could simply trust software distributed by a compromised server.
That creates a classic supply-chain problem:
Trusted server → trusted download → trusted employee → malware execution.
Why Unpatched Systems Remain Such an Attractive Target
Security teams frequently discuss zero-days because they are dramatic.
But attackers often do not need zero-days.
A vulnerability patched months earlier can remain extraordinarily valuable when organizations fail to deploy the update.
Kaspersky noted that the TrueConf vulnerability used by Head Mare had already been addressed, with updates released for supported TrueConf Server versions in August 2025.
Securelist
That means the
The attacker does not care when the vendor released the fix.
The attacker cares about how many vulnerable systems remain online.
The Broader Head Mare Campaign
Head
Kaspersky has documented campaigns against Russian government organizations, construction companies, manufacturers, educational institutions, scientific organizations, energy-sector entities, transportation organizations, and other sectors.
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The
That variety is important.
A mature attacker does not need one perfect attack.
They need several workable paths.
The Human Element Still Matters
Even sophisticated campaigns continue to use social engineering.
Kaspersky reported Head Mare phishing campaigns involving legitimate-looking messages, malicious archives, LNK files, PowerShell execution, decoy documents, and persistence mechanisms.
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This means organizations cannot solve the problem simply by patching TrueConf.
Employees remain part of the attack surface.
A secure server can be undermined by a malicious document.
A well-trained employee can still be compromised by a highly convincing message.
A modern security program therefore needs both technical controls and human awareness.
What Makes This Campaign Particularly Dangerous
The most concerning feature is the attack chain itself.
The attackers can potentially begin with a public-facing application.
Then they can execute commands.
Then they can escalate privileges.
Then they can establish persistence.
Then they can deploy custom malware.
Then they can communicate through infrastructure that may blend into normal network activity.
Each individual step can look manageable.
Together, they form a serious intrusion.
Why SYSTEM Access Should Trigger an Immediate Investigation
When a public-facing Windows server unexpectedly reaches SYSTEM-level execution, organizations should assume the incident may be larger than the original vulnerability.
Security teams should investigate:
Process creation history.
PowerShell activity.
Web-server directories.
New services.
Scheduled tasks.
Registry persistence.
Unexpected administrative accounts.
Modified application files.
Recently created executables.
Outbound network connections.
Authentication events.
Cloud-storage activity.
EDR alerts surrounding the TrueConf process.
The central question should not be:
Was TrueConf vulnerable?
It should be:
What happened after the attacker obtained execution?
Detection Should Focus on Behavior
Traditional antivirus detection may identify known PhantomCore samples.
That is useful, but insufficient.
Attackers can modify binaries.
They can rename files.
They can change infrastructure.
They can rebuild malware.
Behavior is harder to change without affecting the attack itself.
For example, defenders should pay attention to unusual PowerShell execution originating from a TrueConf process, unexpected child processes, suspicious network connections, creation of web-accessible scripts, and abnormal administrative activity.
These behaviors can expose an intrusion even when the malware itself is unknown.
What Organizations Using TrueConf Should Do
Organizations operating TrueConf Server should immediately verify their deployed version and compare it with the vendor’s security guidance.
If an affected or outdated version is discovered, patching should be treated as an urgent security task rather than routine maintenance.
Security teams should also verify that client installers obtained from internal TrueConf infrastructure are legitimate and digitally signed.
Kaspersky specifically recommended checking the authenticity of downloaded client distributions after discovering malicious replacements.
ООО «ИТБ» – Кибербезопасность
Do Not Stop at Patching
Patching closes a vulnerability.
It does not automatically remove an attacker.
If exploitation may already have occurred, organizations need to perform a compromise assessment.
That means examining the server for persistence and malicious activity before declaring the incident resolved.
A compromised server that receives a patch but retains a web shell is still compromised.
A patched server with an attacker-controlled scheduled task is still compromised.
A patched server with stolen credentials can still be a launchpad for another attack.
The Importance of Digital Signatures
The malicious TrueConf installers documented by researchers reportedly lacked valid digital signatures.
ООО «ИТБ» – Кибербезопасность
That creates an opportunity for defenders.
Software distribution systems should verify signatures before allowing applications to execute.
Organizations should also consider application-control policies that prevent unsigned or unexpected binaries from running in sensitive environments.
Software provenance is becoming increasingly important as attackers target trusted distribution channels.
The Cloud Is Not Automatically Safe
OneDrive and other mainstream cloud services provide enormous operational value.
They also provide attackers with infrastructure that defenders cannot simply block without potentially disrupting legitimate business operations.
The answer is not necessarily to block every cloud platform.
Instead, organizations need visibility into:
Which applications communicate with cloud services.
Which processes initiate those connections.
Which accounts are involved.
Whether the traffic is normal for that endpoint.
Whether unusual data transfers occur.
Whether a newly created process suddenly begins communicating externally.
Context is becoming more important than reputation.
What Undercode Say:
1. The Real Target Is Trust
The most interesting part of this campaign is not the malware name.
It is the abuse of trust.
2. Trusted Applications Become Dangerous When Exposed
A legitimate conferencing server can become an attack platform when its security boundary is breached.
- Patching Is Still One of the Strongest Defenses
The TrueConf vulnerability had already been patched, yet vulnerable systems remained attractive targets.
4. Internet-Facing Services Deserve Priority
An outdated internal workstation is concerning.
An outdated internet-facing server can be significantly more dangerous.
5. SYSTEM Access Changes the Incident
Once attackers reach SYSTEM privileges, organizations should move from vulnerability management to incident response.
6. Web Shells Create Persistence
A web shell can allow attackers to return without repeatedly exploiting the original flaw.
7. Custom Malware Shows Operational Maturity
PhantomCore and related tools indicate that the attackers maintain purpose-built capabilities.
8. Malware Evolution Matters
Head Mare has repeatedly modified its tools instead of depending on one static implant.
9. PowerShell Remains Powerful
PowerShell gives attackers access to functionality already present in Windows.
10. Living-off-the-Land Techniques Complicate Detection
When attackers use legitimate system utilities, traditional malware signatures become less effective.
11. Cloud Services Can Become C2 Infrastructure
Communication through trusted platforms can complicate network-based detection.
12. Reputation Alone Is Not Enough
A legitimate domain or cloud provider does not guarantee legitimate behavior.
13. Process Context Matters
Security teams should ask which process initiated a connection, not simply where the connection went.
14. The Parent-Child Relationship Can Reveal Attacks
Unexpected child processes launched by a conferencing server deserve investigation.
15. Persistence Is the
Scheduled tasks, services, registry modifications, and web shells should be aggressively monitored.
16. Supply-Chain Risk Extends the Blast Radius
Compromised software distribution can affect organizations that were never directly attacked.
- Digital Signatures Can Provide a Critical Barrier
Unsigned software should receive greater scrutiny, particularly when downloaded from internal infrastructure.
18. Collaboration Platforms Need Security Ownership
Video conferencing systems should not be treated as low-priority appliances.
19. Security Teams Need Asset Visibility
You cannot patch systems you do not know exist.
20. External Exposure Must Be Measured
Organizations should continuously identify which administrative and application interfaces are internet-accessible.
21. Vulnerability Scanning Needs Context
Finding a vulnerability is not enough.
22. Exploitability Should Drive Priority
Internet-facing vulnerabilities with known exploitation activity should move rapidly through remediation.
23. Detection Should Begin Before the Patch
Organizations should preserve logs and telemetry before changing compromised systems.
24. Incident Response Should Follow Exploitation
A vulnerable server that was exploited requires investigation even after the vulnerability is fixed.
25. Credentials May Become the Next Target
Privileged access obtained from one server can potentially lead to credential theft and lateral movement.
26. Network Segmentation Limits Damage
A conferencing server should not have unrestricted access to sensitive internal systems.
27. Administrative Interfaces Need Extra Protection
Management interfaces should ideally be isolated from the public internet.
28. EDR Telemetry Becomes Extremely Valuable
Process trees can reveal malicious activity that static signatures miss.
29. Logging Must Survive the Incident
Attackers may attempt to remove evidence, making centralized logging essential.
30. Threat Intelligence Adds Context
Known Head Mare infrastructure and malware indicators can help organizations identify related activity.
- Indicators Should Not Become the Entire Strategy
Attackers can rotate infrastructure and rebuild malware.
32. Behavioral Detection Is More Durable
Suspicious execution patterns remain useful even when malware hashes change.
33. Employees Still Need Training
Technical defenses cannot completely eliminate phishing and social engineering.
34. Supply-Chain Verification Should Become Routine
Organizations should verify downloaded software before deployment.
35. Security Teams Should Assume Layered Persistence
Finding one malicious artifact should trigger a search for additional mechanisms.
36. Attackers Think in Chains
Defenders must stop viewing vulnerabilities as isolated events.
37. Initial Access Is Only Chapter One
The most damaging actions often occur after the first compromise.
38. The Lesson Extends Beyond TrueConf
Any internet-facing enterprise application can become the same kind of gateway.
39. Patched Does Not Always Mean Safe
A system may remain compromised after the original vulnerability has been fixed.
40. The Biggest Lesson Is Simple
Every exposed service is part of the security perimeter, whether the organization considers it critical or not.
Deep Analysis
Check for Exposed TrueConf Services
Administrators can begin by identifying whether TrueConf services are exposed externally:
sudo ss -tulpn
For broader asset discovery within an authorized environment:
sudo nmap -sV --open <authorized-host>
Search for Suspicious PowerShell Activity
On Windows systems, defenders should inspect PowerShell operational logs and process creation events.
A useful PowerShell query can begin with:
Get-WinEvent -LogName "Microsoft-Windows-PowerShell/Operational" |
Where-Object {$_.Id -in 4103,4104} |
Select-Object TimeCreated, Id, Message
Investigate Unexpected Scheduled Tasks
Because scheduled-task persistence has appeared in Head Mare activity, defenders should review task creation and suspicious task actions:
Get-ScheduledTask | Select-Object TaskName, TaskPath, State
Then investigate tasks whose actions launch PowerShell, command shells, scripts, or executables from unusual directories.
Search for Suspicious Web Shell Locations
Web-facing servers should be examined for unexpected scripts and recently modified files.
On Linux:
find /var/www /srv/www -type f -mtime -14 -ls
On Windows environments, administrators should inspect the relevant IIS or application directories and compare them against known-good deployments.
Examine Process Relationships
Defenders should look for unusual parent-child relationships.
For example:
Get-CimInstance Win32_Process | Select-Object ProcessId, ParentProcessId, Name, CommandLine
The goal is to determine whether a legitimate conferencing service unexpectedly launches:
powershell.exe
cmd.exe
wscript.exe
cscript.exe
rundll32.exe
mshta.exe
ssh.exe
Unexpected relationships should be investigated rather than automatically dismissed.
Review Outbound Connections
On Windows:
Get-NetTCPConnection |
Where-Object {$_.State -eq "Established"} |
Select-Object LocalAddress,LocalPort,RemoteAddress,RemotePort,OwningProcess
On Linux:
sudo ss -tpn
The objective is to identify processes making unusual external connections.
Compare Installed Files Against Known-Good Versions
Organizations should maintain hashes or trusted software inventories for critical applications.
A basic Windows hash check can be performed with:
Get-FileHash "C:\Path\To\File.exe" -Algorithm SHA256
The resulting hash can then be compared against the vendor’s trusted release information.
Inspect Authentication Events
A compromised server can become useful for credential abuse.
Windows security teams should examine successful and failed authentication events around the suspected compromise window.
Linux administrators can review:
sudo journalctl --since "24 hours ago" | grep -Ei "ssh|authentication|sudo|failed"
Search for Newly Created Services
On Windows:
Get-Service | Sort-Object Status,Name
Unexpected services should be compared against the
Investigate File Modification Timelines
On Linux:
sudo find /etc /opt /usr/local -type f -mtime -7 -ls
The exact directories should be adapted to the organization’s architecture.
Centralize the Evidence
Security logs should be forwarded to a centralized SIEM where attackers cannot easily modify them.
Useful telemetry includes:
Process creation
PowerShell execution
Authentication
Scheduled task creation
Service installation
Network connections
DNS queries
File creation
File modification
EDR alerts
Cloud authentication
Application logs
Containment Comes Before Cleanup
If exploitation is suspected, defenders should isolate the affected server from unnecessary network access before attempting extensive remediation.
The priority should be:
Detect
→ Contain
→ Preserve evidence
→ Investigate
→ Remove persistence
→ Patch
→ Rotate credentials
→ Validate
→ Restore
→ Monitor
The Most Important Defensive Principle
Do not assume that removing the malware file ends the incident.
The attacker may have created another account.
They may have installed another persistence mechanism.
They may have stolen credentials.
They may have moved laterally.
The TrueConf vulnerability is only the beginning of the investigation.
TrueConf Exploitation
✅ Confirmed: Kaspersky has documented Head Mare exploiting the BDU:2025-10114 TrueConf Server vulnerability, including arbitrary command execution.
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Malicious TrueConf Installers
✅ Confirmed: Kaspersky reported compromised TrueConf servers distributing modified client installers and warned organizations to verify digital signatures.
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Head
✅ Confirmed: Kaspersky has documented PhantomCore, PhantomDL, PhantomHeart and other tools associated with Head Mare activity across multiple campaigns.
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Prediction
(+1) More Attacks Against Unpatched Collaboration Servers
Internet-facing collaboration platforms will remain attractive targets because they provide attackers with a direct path into enterprise networks.
Known vulnerabilities will continue to generate successful attacks long after patches become available.
Attackers are likely to continue combining custom malware with legitimate cloud services to complicate detection.
Security teams will increasingly prioritize behavioral detection over simple malware signatures.
Software-signing and supply-chain verification will become more important as attackers target trusted application distribution.
(-1) The Risk Will Not Disappear With a Single Patch
Patching TrueConf alone will not remove an existing web shell, backdoor, stolen credential, or persistence mechanism.
Organizations that treat vulnerability remediation as the end of incident response may leave attackers inside their networks.
Blocking one C2 domain or IP address will not necessarily stop a campaign capable of changing infrastructure.
Final Warning: The Server You Ignore Could Be the Door Attackers Need
The Head Mare activity surrounding TrueConf is a reminder that cybersecurity failures rarely begin with a dramatic alarm.
Sometimes they begin with an overlooked update.
Sometimes with an internet-facing application that nobody thought was especially sensitive.
Sometimes with a legitimate cloud service that appears harmless in network logs.
And sometimes with a server that has quietly remained vulnerable for months.
The critical lesson is not simply to patch TrueConf.
It is to understand the entire attack chain.
A vulnerable application can provide access. A web shell can provide persistence. Custom backdoors can provide control. Trusted cloud services can provide cover. And stolen credentials can turn one compromised server into an entire network problem.
That is why modern defense has to operate beyond the vulnerability itself.
Patch the exposed service. Verify the software. Monitor the behavior. Hunt for persistence. Investigate privilege escalation. Protect credentials. Segment critical systems. And never assume that a patched server is clean simply because the vulnerability has been closed.
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