CVE-2026-2402: Authentication Bypass Vulnerability

CVE-2026-2402 Overview

CVE-2026-2402 is an Improper Restriction of Excessive Authentication Attempts vulnerability (CWE-307) that allows attackers to gain unauthorized access to user accounts. The vulnerability exists due to missing rate limiting or account lockout mechanisms, enabling attackers to perform an arbitrary number of authentication attempts with different credentials across multiple endpoints in a sequence of requests.

Critical Impact

Attackers can perform brute-force attacks against authentication endpoints without restriction, potentially compromising user accounts and gaining unauthorized access to protected systems.

Affected Products

• Schneider Electric Industrial Control Products (refer to Schneider Electric Security Notice for specific product versions)

Discovery Timeline

• 2026-04-14 - CVE CVE-2026-2402 published to NVD
• 2026-04-14 - Last updated in NVD database

Technical Details for CVE-2026-2402

Vulnerability Analysis

This vulnerability stems from a fundamental weakness in authentication controls. The affected system fails to implement proper restrictions on authentication attempts, allowing attackers to execute brute-force or credential stuffing attacks without being blocked or throttled. The network-accessible nature of the vulnerability means that remote attackers can target authentication endpoints from anywhere with network connectivity to the affected system.

The attack requires no prior authentication or special privileges, making it accessible to any network-connected attacker. The vulnerability impacts multiple authentication endpoints, meaning attackers can distribute their attempts across different request paths to evade basic detection methods that might only monitor single endpoints.

Root Cause

The root cause of CVE-2026-2402 is the absence of proper authentication rate limiting and account lockout mechanisms. The application does not track failed authentication attempts or enforce delays/lockouts after a threshold of failed attempts. This allows attackers to systematically test credential combinations without any defensive countermeasures activating.

Common implementations that would mitigate this vulnerability include:

• Account lockout after a configurable number of failed attempts
• Progressive delays between authentication attempts
• CAPTCHA challenges after failed attempts
• IP-based rate limiting on authentication endpoints

Attack Vector

The attack is network-based, requiring no user interaction or authenticated access. An attacker can exploit this vulnerability by sending repeated authentication requests to the affected endpoints with different credential combinations. The attack can be automated using common tools and scripts, making it practical for attackers to test large credential lists or dictionary attacks.

The vulnerability is particularly concerning in industrial control system environments where compromised accounts could lead to manipulation of critical operational systems. Attackers may distribute attempts across multiple endpoints mentioned in the vulnerability description, potentially evading simple single-endpoint monitoring.

Detection Methods for CVE-2026-2402

Indicators of Compromise

• High volume of failed authentication attempts from single or multiple source IPs
• Rapid sequential authentication requests targeting multiple user accounts
• Authentication attempts using known credential lists or common password patterns
• Unusual geographic distribution of authentication attempts
• Authentication traffic outside normal business hours or usage patterns

Detection Strategies

• Implement authentication log monitoring to detect unusual volumes of login attempts
• Configure alerting for multiple failed authentication attempts within short time windows
• Deploy network-based intrusion detection rules for brute-force attack patterns
• Monitor for credential stuffing indicators such as sequential attempts across multiple accounts
• Correlate authentication events across multiple endpoints to detect distributed attacks

Monitoring Recommendations

• Enable verbose logging on all authentication endpoints and centralize logs for analysis
• Establish baseline authentication metrics and alert on significant deviations
• Implement real-time alerting for brute-force attack indicators
• Monitor authentication endpoint response times for signs of automated attacks

How to Mitigate CVE-2026-2402

Immediate Actions Required

• Review the Schneider Electric Security Notice for vendor-specific guidance
• Implement network-level rate limiting on authentication endpoints
• Enable account lockout policies where supported
• Restrict network access to authentication endpoints to trusted networks only
• Deploy Web Application Firewalls (WAF) with brute-force protection rules

Patch Information

Refer to the Schneider Electric Security Notice SEVD-2026-104-01 for official patch information and remediation guidance. Contact Schneider Electric support for specific firmware or software updates addressing this vulnerability.

Workarounds

• Implement network segmentation to restrict access to affected authentication endpoints
• Deploy external rate limiting solutions such as reverse proxies or WAFs in front of vulnerable systems
• Use VPN or jump servers to limit direct network access to industrial control systems
• Enable multi-factor authentication where supported to reduce impact of compromised credentials
• Implement IP allowlisting for administrative authentication endpoints

# Example: Rate limiting with iptables (adjust interface and limits as needed)
# Limit new connections to authentication port to 5 per minute per 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 5 -j DROP