CVE-2026-31904: WebSocket API DoS Vulnerability

CVE-2026-31904 Overview

CVE-2026-31904 is a vulnerability affecting the WebSocket Application Programming Interface which lacks restrictions on the number of authentication requests. This absence of rate limiting enables attackers to conduct denial-of-service attacks by suppressing or mis-routing legitimate charger telemetry, or conduct brute-force attacks to gain unauthorized access. The vulnerability is classified under CWE-307 (Improper Restriction of Excessive Authentication Attempts).

Critical Impact

Attackers can exploit the missing rate limiting to disrupt electric vehicle charging infrastructure operations through denial-of-service attacks or gain unauthorized system access via brute-force credential attacks.

Affected Products

• CTEK Electric Vehicle Charging Systems (WebSocket API component)
• CTEK Charger Telemetry Systems
• Industrial Control Systems utilizing the vulnerable WebSocket API

Discovery Timeline

• 2026-03-20 - CVE CVE-2026-31904 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2026-31904

Vulnerability Analysis

This vulnerability stems from a fundamental security design flaw in the WebSocket API implementation used in electric vehicle charging infrastructure. The API endpoint responsible for handling authentication requests does not implement any mechanism to limit the rate or frequency of authentication attempts. This allows an attacker to send an unlimited number of authentication requests in rapid succession without being blocked or throttled.

The impact of this vulnerability is significant in operational technology (OT) environments where reliable communication between chargers and management systems is critical. An attacker could exploit this flaw to overwhelm the authentication service, causing legitimate charger telemetry data to be dropped or misdirected, effectively creating a denial-of-service condition that could disrupt charging operations across an entire network.

Root Cause

The root cause is the absence of rate limiting controls on the WebSocket API authentication endpoint. The implementation fails to track authentication attempts per client or implement any throttling mechanism, violating secure design principles for authentication systems. This is classified as CWE-307: Improper Restriction of Excessive Authentication Attempts.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker with network access to the WebSocket API endpoint can exploit this vulnerability in two primary ways:

Denial-of-Service Attack: By flooding the authentication endpoint with requests, an attacker can exhaust server resources, causing legitimate authentication requests to fail. This disrupts the telemetry communication between charging stations and central management systems, potentially affecting charging operations and monitoring capabilities.

Brute-Force Attack: The lack of rate limiting allows an attacker to systematically attempt credential combinations at high speed without triggering lockouts or delays. If successful, this could grant unauthorized access to the charging infrastructure management interface, enabling further malicious actions such as manipulating charger configurations or accessing sensitive operational data.

Detection Methods for CVE-2026-31904

Indicators of Compromise

• Abnormally high volume of WebSocket authentication requests from single IP addresses or ranges
• Repeated authentication failures in system logs with rapid succession timestamps
• Telemetry data gaps or interruptions coinciding with authentication request spikes
• Unusual network traffic patterns to WebSocket API endpoints

Detection Strategies

• Implement network monitoring to detect high-frequency authentication request patterns to WebSocket endpoints
• Configure intrusion detection systems (IDS) to alert on authentication request rates exceeding normal operational thresholds
• Monitor for sequential authentication failures that indicate potential brute-force activity
• Deploy application-layer monitoring to track WebSocket connection and authentication metrics

Monitoring Recommendations

• Enable detailed logging for all WebSocket API authentication events with timestamps and source IPs
• Establish baseline metrics for normal authentication request volumes and configure alerts for anomalies
• Implement network flow analysis to identify potential DoS attack patterns targeting the authentication service
• Regularly review authentication logs for patterns indicative of brute-force attempts

How to Mitigate CVE-2026-31904

Immediate Actions Required

• Contact CTEK support for firmware updates or patches addressing this vulnerability
• Implement network-level rate limiting using firewalls or load balancers to restrict authentication request frequency
• Segment affected charging infrastructure from general network access where possible
• Enable enhanced logging and monitoring for WebSocket API endpoints

Patch Information

Consult the CISA ICS Advisory for official remediation guidance. Additional technical details are available in the GitHub CSAF File. For vendor-specific updates and support, visit the CTEK Support Page.

Workarounds

• Deploy a reverse proxy or Web Application Firewall (WAF) in front of the WebSocket API with rate limiting configured
• Implement IP-based access controls to restrict WebSocket API access to known, trusted networks
• Enable account lockout policies where supported to mitigate brute-force attack impact
• Consider temporarily disabling WebSocket API network exposure until patches are applied, if operationally feasible

# Example: Network-level rate limiting using iptables
# Limit new WebSocket connections to 10 per minute per source IP
iptables -A INPUT -p tcp --dport 443 -m state --state NEW -m recent --set
iptables -A INPUT -p tcp --dport 443 -m state --state NEW -m recent --update --seconds 60 --hitcount 10 -j DROP