CERT Polska: a second Polish CHP plant was shut down on 29 December 2025 through the distribution operator's private APN — the first real-world use of that path into an OT network
CERT Polska published a follow-up analysis on 2026-08-08 of the coordinated 29 December 2025 attacks on Poland's energy sector, adding a victim its January report did not carry: a smaller combined heat and power plant supplying heat to roughly 50,000 residents, whose industrial control systems came under attack at about 07:00 that morning (CERT Polska, 2026-08-08). The analysis took more than three months, which is why the case was held back from the initial report published on 30 January 2026 (CERT Polska, 2026-08-08). The head of CERT Polska, Marcin Dudek, presented the case at DEF CON in parallel with publication (CERT Polska, 2026-08-08). The report carries no actor attribution.
The finding that generalises beyond Poland is the access path. Substations that connect renewable generation to the distribution grid commonly carry cellular routers whose SIM cards sit in a private APN — a carrier-operated private mobile network the distribution system operator uses to reach the remote terminal unit at each site, in this case over DNP3.0 (CERT Polska, 2026-08-08). The operator's requirements covered the serial path to the RTU but said nothing about the router's own administrative interface, so the Teltonika RUTX50 at the compromised wind farm sat with its serial link to the RTU on one interface and an Ethernet link into a VLAN behind the already-compromised central firewall on the other (CERT Polska, 2026-08-08). CERT Polska states this is the first instance it knows of in which a private APN was the route into an OT network, made possible by a configuration that let arbitrary devices inside the APN talk to one another — a configuration its surveys found common in Poland and which it believes is widely deployed in other countries (CERT Polska, 2026-08-08).
The chain ran as follows. Every compromised wind-farm substation in the original wave — more than 30 grid connection points — used a FortiGate as both VPN concentrator and firewall, with the VPN interface reachable from the internet and accepting accounts defined on the device itself without multi-factor authentication; the attacker held administrative privileges on the device and likely used them to obtain a VPN account with reach across all network segments (CERT Polska, 2026-08-08). From inside, the attacker logged into the Teltonika router over SSH repeatedly during December 2025 and tunnelled from it into the private APN; how the router password was obtained could not be determined, and whether a flaw in the device was used is likewise unresolved (CERT Polska, 2026-08-08). From 18 December the attacker scanned the APN for VNC and HTTP services and for the S7 and Modbus industrial protocols, and found a WAGO PFC200 controller exposing a web administration interface on its WAN side, reachable from the APN and still on the default credentials for the admin account; SSH was not enabled on that interface by default, and the sequence in the carrier's logs indicates the attacker enabled it through the web interface before tunnelling onward into the heat plant's OT network, to which the controller had connectivity for both the SCADA systems and the segments holding process-control devices (CERT Polska, 2026-08-08).
Reconnaissance inside the plant ran from 18 to 25 December. Repeated attempts to reach the firewall's LAN-side web interface using the account names admin, user and a username belonging to the company that deploys telecontrol systems at renewable sites all failed, and were retried three days later without success (CERT Polska, 2026-08-08). On Sunday 21 December, eight days before the attack, the attacker scanned for S7 on 102/TCP, Modbus on 502/TCP, CODESYS on 11740/TCP and RTSP on 554/TCP alongside RDP, VNC and web services — and in one subnet the scan began at the address of the SCADA system itself, which CERT Polska reads as evidence of earlier reconnaissance having already identified the high-value targets (CERT Polska, 2026-08-08). On Christmas Day the attacker established successful S7 connections to three Siemens PLCs, most plausibly to prepare the destructive step (CERT Polska, 2026-08-08).
On 29 December activity inside the plant network ran from about 05:30 to about 10:10, meaning the operator's recovery work beginning around 07:30 started while the attacker was still present (CERT Polska, 2026-08-08). The first action after tunnelling through the WAGO controller was to open the SCADA server's web interface, then reach an S7-300 over the S7 protocol, repeating the sequence against an S7-1200 and an S7-1500 (CERT Polska, 2026-08-08). According to statements from plant personnel the PLCs were switched to STOP mode and protected with a password blocking both operating-state changes and control-logic modification, shutting down the steam turbine and the process-water treatment system and interrupting cogeneration; prompt operator response held it to a short outage with no interruption to customer heat or electricity supply (CERT Polska, 2026-08-08). The attacker also reconfigured seven Moxa serial device servers and three Moxa switches — factory reset, password changed, addresses moved to unreachable values such as 127.0.0.1 — and the timing of the HTTP requests supports a high-confidence assessment that this was automated (CERT Polska, 2026-08-08). Connections to two ABB ACS variable frequency drives were observed with no determinable effect, and attempts against Schneider Electric ATV 6xx drives failed because the attacker targeted 80/TCP while those interfaces listened elsewhere (CERT Polska, 2026-08-08).
Two recovery lessons sit in the anti-forensics. The attacker corrupted the partition table of the WAGO controller used as the gateway, and the operator's own factory reset did not repair it, leaving the device unbootable and its logs unrecoverable; the Teltonika router was factory-reset about thirty minutes after the last plant activity and its address set to 127.0.0.1, and the FortiGate was factory-reset last of all, destroying the logs from the initial entry point (CERT Polska, 2026-08-08). The investigation only recovered router evidence because RutOS versions before 7.07 keep the event database through a factory reset (CERT Polska, 2026-08-08). On the plant side, restoring the Siemens controllers to factory settings and reloading logic backups shortened the outage but deleted the controllers' own logs, and Siemens ProductCERT confirmed they could not be recovered (CERT Polska, 2026-08-08).
Triage: an engineering contractor doing legitimate remote maintenance also logs into a cellular router and reaches PLCs over S7, so neither event alone separates the two. The discriminators here are direction and sequence — the session enters from the APN side of a device whose administrative interface was never meant to face it, port scanning precedes the PLC access by days, and the run-state change is followed within minutes by configuration writes to unrelated serial servers and switches. This plant's operators initially read the shutdown as contractor error during scheduled maintenance and reported it for information only; CERT Polska opened an investigation anyway because it knew of similar events, which is what turned an unexplained failure into a confirmed intrusion (CERT Polska, 2026-08-08).
To the best of our knowledge, the use of a private APN to gain access to the OT network was the first instance of this attack vector being observed in a real-world cyberattack.
The attack was made possible, among other factors, by a misconfiguration that allowed arbitrary devices within the private APN network to communicate with one another.
Surveys conducted among organizations using similar solutions indicated that this configuration was commonly encountered in Poland.
Defender actions
- Audit the client-isolation setting on every private APN your OT estate reaches, and enable it: this intrusion crossed from a wind-farm substation to an unrelated heat plant only because arbitrary devices inside the operator's private APN could open connections to each other.
- Enumerate what answers on the APN-facing interface of each device connected to that APN and close or re-credential its administrative services — the pivot device here was a WAGO PFC200 whose WAN-side web interface was reachable from the APN on default 'admin' credentials, and SSH was then turned on through that interface.
ATT&CK mapping
9 techniques mapped from the cited reporting · MITRE ATT&CK v19.1
Initial Access TA0001
T1078Valid Accounts
Adversaries may obtain and abuse credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Compromised credentials may be used to bypass access controls placed on various resources on systems within the network and may even be used for persistent access to remote systems and externally available services, such as VPNs, Outlook Web Access, network devices, and remote desktop. Compromised credentials may also grant an adversary increased privilege to specific systems or access to restricted areas of the network. Adversaries may choose not to use malware or tools in conjunction with the legitimate access those credentials provide to make it harder to detect their presence.
T1078.001Valid Accounts: Default Accounts
Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Default accounts are those that are built-into an OS, such as the Guest or Administrator accounts on Windows systems. Default accounts also include default factory/provider set accounts on other types of systems, software, or devices, including the root user account in AWS, the root user account in ESXi, and the default service account in Kubernetes.
T1133External Remote Services
Adversaries may leverage external-facing remote services to initially access and/or persist within a network. Remote services such as VPNs, Citrix, and other access mechanisms allow users to connect to internal enterprise network resources from external locations. There are often remote service gateways that manage connections and credential authentication for these services. Services such as Windows Remote Management and VNC can also be used externally.
Persistence TA0003
T1078Valid Accounts
Adversaries may obtain and abuse credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Compromised credentials may be used to bypass access controls placed on various resources on systems within the network and may even be used for persistent access to remote systems and externally available services, such as VPNs, Outlook Web Access, network devices, and remote desktop. Compromised credentials may also grant an adversary increased privilege to specific systems or access to restricted areas of the network. Adversaries may choose not to use malware or tools in conjunction with the legitimate access those credentials provide to make it harder to detect their presence.
T1078.001Valid Accounts: Default Accounts
Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Default accounts are those that are built-into an OS, such as the Guest or Administrator accounts on Windows systems. Default accounts also include default factory/provider set accounts on other types of systems, software, or devices, including the root user account in AWS, the root user account in ESXi, and the default service account in Kubernetes.
T1133External Remote Services
Adversaries may leverage external-facing remote services to initially access and/or persist within a network. Remote services such as VPNs, Citrix, and other access mechanisms allow users to connect to internal enterprise network resources from external locations. There are often remote service gateways that manage connections and credential authentication for these services. Services such as Windows Remote Management and VNC can also be used externally.
Privilege Escalation TA0004
T1078Valid Accounts
Adversaries may obtain and abuse credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Compromised credentials may be used to bypass access controls placed on various resources on systems within the network and may even be used for persistent access to remote systems and externally available services, such as VPNs, Outlook Web Access, network devices, and remote desktop. Compromised credentials may also grant an adversary increased privilege to specific systems or access to restricted areas of the network. Adversaries may choose not to use malware or tools in conjunction with the legitimate access those credentials provide to make it harder to detect their presence.
T1078.001Valid Accounts: Default Accounts
Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Default accounts are those that are built-into an OS, such as the Guest or Administrator accounts on Windows systems. Default accounts also include default factory/provider set accounts on other types of systems, software, or devices, including the root user account in AWS, the root user account in ESXi, and the default service account in Kubernetes.
Stealth TA0005
T1070Indicator Removal
Adversaries may selectively delete or modify artifacts generated to reduce indications of their presence and blend in with legitimate activity. Rather than broadly removing evidence, adversaries may target specific artifacts that appear anomalous or are likely to draw scrutiny, while leaving sufficient data intact to maintain the appearance of normal system behavior.
T1078Valid Accounts
Adversaries may obtain and abuse credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Compromised credentials may be used to bypass access controls placed on various resources on systems within the network and may even be used for persistent access to remote systems and externally available services, such as VPNs, Outlook Web Access, network devices, and remote desktop. Compromised credentials may also grant an adversary increased privilege to specific systems or access to restricted areas of the network. Adversaries may choose not to use malware or tools in conjunction with the legitimate access those credentials provide to make it harder to detect their presence.
T1078.001Valid Accounts: Default Accounts
Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Default accounts are those that are built-into an OS, such as the Guest or Administrator accounts on Windows systems. Default accounts also include default factory/provider set accounts on other types of systems, software, or devices, including the root user account in AWS, the root user account in ESXi, and the default service account in Kubernetes.
Discovery TA0007
T1046Network Service Discovery
Adversaries may attempt to get a listing of services running on remote hosts and local network infrastructure devices, including those that may be vulnerable to remote software exploitation. Common methods to acquire this information include port, vulnerability, and/or wordlist scans using tools that are brought onto a system.
Lateral Movement TA0008
T1021.004Remote Services: SSH
Adversaries may use Valid Accounts to log into remote machines using Secure Shell (SSH). The adversary may then perform actions as the logged-on user.
Command and Control TA0011
T1572Protocol Tunneling
Adversaries may tunnel network communications to and from a victim system within a separate protocol to avoid detection/network filtering and/or enable access to otherwise unreachable systems. Tunneling involves explicitly encapsulating a protocol within another. This behavior may conceal malicious traffic by blending in with existing traffic and/or provide an outer layer of encryption (similar to a VPN). Tunneling could also enable routing of network packets that would otherwise not reach their intended destination, such as SMB, RDP, or other traffic that would be filtered by network appliances or not routed over the Internet.
Impact TA0040
T1531Account Access Removal
Adversaries may interrupt availability of system and network resources by inhibiting access to accounts utilized by legitimate users. Accounts may be deleted, locked, or manipulated (ex: changed credentials, revoked permissions for SaaS platforms such as Sharepoint) to remove access to accounts. Adversaries may also subsequently log off and/or perform a System Shutdown/Reboot to set malicious changes into place.
T1561.002Disk Wipe: Disk Structure Wipe
Adversaries may corrupt or wipe the disk data structures on a hard drive necessary to boot a system; targeting specific critical systems or in large numbers in a network to interrupt availability to system and network resources.
AI-generated · no human review · this permalink is the shareable record for the finding · verify operationally critical claims against the linked primary source.