CVE-2026-44107 Overview
CVE-2026-44107 is a high-severity denial-of-service vulnerability affecting a charging controller that exposes Modbus TCP functionality through the CharxModbusServer service. An unauthenticated remote attacker can send a Modbus TCP command that forces the controller to reboot. The flaw is classified under CWE-749: Exposed Dangerous Method or Function. Exploitation requires only network reachability to the listening Modbus port and no credentials or user interaction. The vulnerability is documented in the CERT-VDE Advisory VDE-2026-008.
Critical Impact
Any attacker with network access to the exposed Modbus TCP port can repeatedly reboot the charging controller, disrupting charging operations without authentication.
Affected Products
- Charging controller running CharxModbusServer with Modbus TCP functionality enabled
- Refer to the CERT-VDE Advisory VDE-2026-008 for specific product and firmware versions
Discovery Timeline
- 2026-07-30 - CVE-2026-44107 published to NVD
- 2026-07-30 - Last updated in NVD database
Technical Details for CVE-2026-44107
Vulnerability Analysis
The charging controller exposes an administrative reboot function through its Modbus TCP interface. When Modbus is enabled, the CharxModbusServer process listens on a TCP port and accepts requests without validating the identity of the requester. The reboot command is available as an exposed dangerous method, meaning it is reachable through normal protocol operations rather than a restricted management channel. An attacker who can reach the port can issue the reboot command and interrupt device operation. Repeating the request produces a sustained denial-of-service condition against the charging infrastructure.
Root Cause
The root cause is an exposed dangerous function reachable through an unauthenticated protocol interface, consistent with CWE-749. Modbus TCP does not provide native authentication, and the controller does not enforce an additional authorization layer before honoring the reboot instruction. Any client capable of establishing a TCP session with CharxModbusServer gains equivalent privilege to trigger a device restart.
Attack Vector
Exploitation occurs over the network. The attacker requires TCP reachability to the port on which CharxModbusServer listens, typically TCP/502 for Modbus. No credentials, tokens, or user interaction are required. The attack targets availability only; the vulnerability does not directly expose configuration data, cryptographic material, or firmware. Impact scales with attacker persistence, because each successful request forces another reboot cycle.
No public proof-of-concept code has been released. Detailed protocol-level exploitation guidance is available in the CERT-VDE Advisory VDE-2026-008.
Detection Methods for CVE-2026-44107
Indicators of Compromise
- Unexpected reboot cycles in charging controller logs correlated with inbound Modbus TCP sessions
- Modbus TCP connections to CharxModbusServer originating from IP addresses outside the operational technology (OT) management network
- Repeated short-lived TCP sessions to the Modbus port followed by controller unavailability
Detection Strategies
- Monitor Modbus TCP traffic to charging controllers and alert on function codes that map to administrative or reboot operations
- Correlate device availability loss events with preceding Modbus TCP writes from the same source
- Baseline expected Modbus client IPs and flag any new or external source addresses initiating sessions
Monitoring Recommendations
- Ingest charging controller and firewall logs into a central analytics platform for correlation between reboot events and network activity
- Enable network flow logging on OT segment boundaries to identify unauthorized Modbus TCP access attempts
- Alert on any Modbus session originating from IT networks, guest networks, or the internet
How to Mitigate CVE-2026-44107
Immediate Actions Required
- Disable Modbus TCP functionality on the charging controller if it is not required for operations
- Restrict access to the CharxModbusServer listening port using firewall rules that permit only trusted management hosts
- Segment charging controllers into a dedicated OT VLAN isolated from general enterprise and internet-facing networks
- Review controller logs for prior unexplained reboots that may indicate exploitation attempts
Patch Information
Refer to the CERT-VDE Advisory VDE-2026-008 for vendor-supplied firmware updates and remediation guidance. Apply the vendor-recommended firmware version once available and validate configurations after upgrade.
Workarounds
- Close the Modbus TCP port at the network perimeter and at any intermediate firewall between the controller and untrusted networks
- Place the charging controller behind a Modbus-aware gateway that enforces source IP allowlisting and function code filtering
- Where operationally feasible, keep Modbus functionality disabled until a patched firmware version is installed
# Example iptables rule restricting Modbus TCP (port 502) to a trusted management host
iptables -A INPUT -p tcp --dport 502 -s 10.10.20.5 -j ACCEPT
iptables -A INPUT -p tcp --dport 502 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
