CVE-2026-31903: WebSocket API DoS Vulnerability

CVE-2026-31903 Overview

CVE-2026-31903 is a vulnerability in a WebSocket Application Programming Interface that lacks restrictions on the number of authentication requests. This absence of rate limiting creates a significant security gap that allows attackers to conduct denial-of-service (DoS) attacks by suppressing or mis-routing legitimate charger telemetry, or perform brute-force attacks to gain unauthorized access to the system.

Critical Impact

Attackers can exploit this vulnerability to disrupt critical infrastructure operations by overwhelming authentication endpoints, potentially disrupting electric vehicle charging station telemetry and gaining unauthorized system access through brute-force credential attacks.

Affected Products

• WebSocket API authentication endpoints for EV charging infrastructure
• Industrial Control Systems (ICS) utilizing the affected WebSocket implementation
• Operational Technology (OT) systems referenced in CISA ICS Advisory

Discovery Timeline

• March 20, 2026 - CVE-2026-31903 published to NVD
• March 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-31903

Vulnerability Analysis

This vulnerability is classified under CWE-307 (Improper Restriction of Excessive Authentication Attempts). The WebSocket API implementation fails to implement proper rate limiting controls on authentication requests, leaving the system vulnerable to two primary attack scenarios.

In a denial-of-service context, an attacker can flood the authentication endpoint with requests, consuming server resources and preventing legitimate users or devices from authenticating. For electric vehicle charging infrastructure, this could result in chargers becoming unable to communicate telemetry data or receive operational commands.

The brute-force attack scenario presents an even more concerning threat. Without rate limiting, attackers can rapidly iterate through password combinations or authentication tokens until valid credentials are discovered, potentially granting unauthorized access to critical infrastructure management systems.

Root Cause

The root cause of CVE-2026-31903 is the absence of authentication rate limiting mechanisms in the WebSocket API. Proper implementation would include request throttling, account lockout policies, and connection rate limits to prevent abuse. The vulnerable implementation accepts an unlimited number of authentication attempts without any protective countermeasures, violating fundamental security principles for authentication systems.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction to exploit. An attacker with network access to the WebSocket API endpoint can initiate the attack remotely. The exploitation process involves establishing WebSocket connections to the target API and sending rapid, repeated authentication requests.

For DoS attacks, the attacker aims to exhaust server resources by overwhelming the authentication handler with connection requests. For brute-force attacks, the attacker systematically attempts credential combinations at high speed, taking advantage of the lack of rate limiting to test thousands of passwords per minute.

The vulnerability is particularly concerning in ICS/OT environments where disruption to charger telemetry could impact critical operations and safety monitoring systems. Technical details and exploitation mechanics are documented in the CISA ICS Advisory ICSA-26-078-08.

Detection Methods for CVE-2026-31903

Indicators of Compromise

• Abnormally high volume of WebSocket connection attempts from single IP addresses or ranges
• Rapid succession of authentication failures followed by sudden successful authentication
• Unusual traffic patterns to WebSocket API endpoints outside normal operational hours
• Degraded system performance or unavailability of authentication services

Detection Strategies

• Implement network monitoring to detect anomalous spikes in WebSocket traffic to authentication endpoints
• Deploy intrusion detection rules that alert on excessive authentication failures from single sources
• Monitor application logs for patterns indicating brute-force attempts (e.g., >100 auth attempts per minute per source)
• Use behavioral analytics to establish baseline authentication patterns and detect deviations

Monitoring Recommendations

• Enable detailed logging on all WebSocket API authentication endpoints
• Configure SIEM alerts for authentication anomalies and potential DoS conditions
• Monitor network bandwidth and connection counts to WebSocket services
• Implement real-time dashboards tracking authentication success/failure ratios

How to Mitigate CVE-2026-31903

Immediate Actions Required

• Implement rate limiting on all WebSocket authentication endpoints (recommended: 5 attempts per minute per source)
• Deploy Web Application Firewall (WAF) rules to block excessive connection attempts
• Enable account lockout policies after a defined number of failed authentication attempts
• Segment network access to restrict exposure of WebSocket APIs to authorized networks only

Patch Information

For specific patch information and remediation guidance, organizations should consult the CISA ICS Advisory ICSA-26-078-08 and the CSAF resource on GitHub. Contact the affected product vendor directly for firmware or software updates that address this vulnerability.

Workarounds

• Deploy a reverse proxy with rate limiting capabilities in front of the WebSocket API
• Implement IP-based access control lists to restrict authentication endpoint access
• Use CAPTCHA or proof-of-work challenges after multiple failed authentication attempts
• Consider implementing multi-factor authentication to reduce brute-force attack effectiveness

# Example nginx rate limiting configuration for WebSocket endpoints
# Add to nginx.conf or appropriate server block

limit_req_zone $binary_remote_addr zone=ws_auth:10m rate=5r/m;

location /ws/auth {
    limit_req zone=ws_auth burst=3 nodelay;
    limit_req_status 429;
    proxy_pass http://websocket_backend;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
}