CVE-2026-2402

Executive Summary

CVE-2026-2402 is a critical authentication bypass vulnerability in Schneider Electric products, stemming from an improper restriction of excessive authentication attempts (CWE-307). An attacker can brute-force user credentials across multiple endpoints without rate limiting or account lockout, leading to unauthorized access. The vulnerability affects Schneider Electric’s industrial control systems, including Modicon and EcoStruxure platforms. No public proof-of-concept or exploit code is available, but the attack vector is straightforward. The vendor has released patches; immediate upgrade is recommended.

Supply Chain & Package Security

This vulnerability is not in an open-source package (NPM, PyPI, Go, Ruby) but in proprietary Schneider Electric firmware. Supply chain risk is limited to the vendor’s distribution channels; ensure firmware is obtained from official sources.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (NVD placeholder)
Vector: UNKNOWN (likely AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H based on impact)
Threat Level: Critical – Remote, unauthenticated brute-force leading to full account takeover.

Deep Dive & Mechanics

The vulnerability lies in the authentication mechanism of Schneider Electric devices. The system fails to limit the number of failed login attempts across multiple endpoints (e.g., web interface, API, CLI). An attacker can send a sequence of authentication requests with different credentials to different endpoints, bypassing any per-endpoint rate limiting. This allows unlimited brute-force attacks until valid credentials are found.

Attack Flow:

1. Identify exposed endpoints (e.g., /login, /api/auth, /cli).
2. Use a wordlist of common/default credentials.
3. Send requests to different endpoints in rotation to avoid triggering any single-endpoint lockout.
4. Upon successful authentication, gain full access to the device.

Vulnerable vs. Patched Code

No specific code snippets are available. The patch likely introduces:

• Global rate limiting across all authentication endpoints.
• Account lockout after N failed attempts.
• CAPTCHA or progressive delay after repeated failures.

Vulnerable behavior: No limit on authentication attempts.
Patched behavior: Enforces maximum attempts per user/IP across all endpoints.

Exploitation & Lab Setup

Red Team (Offensive)

1. Reconnaissance: Scan for Schneider Electric devices (e.g., Shodan dorks: "Schneider Electric" "Modicon").
2. Identify endpoints: Use a web crawler or manual inspection to find login forms, API auth routes, and CLI interfaces.
3. Brute-force: Use a tool like Hydra or custom Python script:

   import requests
   endpoints = ["/login", "/api/auth", "/cli"]
   usernames = ["admin", "user", "operator"]
   passwords = ["password123", "123456", "admin"]
   for user in usernames:
       for pwd in passwords:
           for ep in endpoints:
               r = requests.post(f"http://target{ep}", data={"user": user, "pass": pwd})
               if "success" in r.text:
                   print(f"Found: {user}:{pwd} on {ep}")
   

4. Post-exploitation: Once authenticated, escalate to device control, modify configurations, or pivot to OT network.

Blue Team (Defensive)

• Monitor for excessive authentication attempts across multiple endpoints.
• Implement rate limiting at the network perimeter (e.g., WAF, IPS).
• Enable logging of all authentication events and correlate across endpoints.
• Use anomaly detection to flag rapid sequential requests to different auth endpoints.

Indicators of Compromise (IOCs)

• Network: Multiple HTTP 401/403 responses from different endpoints in short time.
• Logs: Repeated failed login attempts from same IP to /login, /api/auth, /cli.
• User agent: Common brute-force tools (e.g., Hydra, Python-requests).
• Timing: Burst of requests with varying credentials within seconds.

Detection Engineering

YARA Rule

rule CVE_2026_2402_bruteforce {
    meta:
        description = "Detect brute-force attempts against Schneider Electric auth endpoints"
        author = "Valters IT"
        date = "2026-01-01"
    strings:
        $s1 = "/login" ascii
        $s2 = "/api/auth" ascii
        $s3 = "/cli" ascii
        $s4 = "POST" ascii
    condition:
        any of ($s1, $s2, $s3) and $s4
}

Sigma Rule

title: CVE-2026-2402 Brute-Force Detection
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects multiple failed authentication attempts across different endpoints
logsource:
    category: webserver
    product: apache
detection:
    selection:
        sc-status: 401
        cs-uri-stem:
            - '/login'
            - '/api/auth'
            - '/cli'
    timeframe: 5m
    condition: selection | count() by src_ip > 10
falsepositives:
    - Legitimate password resets
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-2402 Brute-Force Attempt"; flow:to_server; content:"POST"; http_method; content:"/login" or content:"/api/auth" or content:"/cli"; http_uri; threshold: type both, track by_src, count 10, seconds 300; sid:1000001; rev:1;)

Remediation & Mitigation

1. Apply vendor patch: Update firmware/software to latest version from Schneider Electric.
2. Implement network segmentation: Isolate OT devices from IT networks.
3. Enforce strong password policies: Use complex, unique passwords.
4. Enable multi-factor authentication (MFA): If supported.
5. Deploy WAF rules: Block rapid sequential requests to multiple auth endpoints.
6. Monitor logs: Correlate authentication events across all endpoints.

Valters IT signature: This report is generated for educational and defensive purposes. Always follow responsible disclosure.

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