CVE-2026-2403

Executive Summary

CVE-2026-2403 is a vulnerability in Schneider Electric products that allows an authenticated Web Admin user to truncate Event and Data Logs by sending a crafted POST request to the /logsettings endpoint. This improper validation of specified quantity (CWE-1284) directly impacts log integrity, making it possible for an attacker to hide malicious activity by removing log entries. The vulnerability has a CVSS score of 0.0 (likely unassigned or placeholder), but the impact on forensic analysis and incident response is significant. No public exploit code or PoC is available at this time, but the attack vector is clear and requires only Web Admin privileges.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects Schneider Electric’s proprietary firmware and web interface components.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (placeholder/unassigned)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: High (Web Admin)
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: High (log truncation)
• Availability Impact: None
• Threat Level: Medium (due to required privileges but high integrity impact)

Deep Dive & Mechanics

The vulnerability resides in the web interface of Schneider Electric devices. The /logsettings endpoint is used to configure logging parameters, including the maximum number of log entries or the retention period. The application fails to properly validate the quantity parameter in the POST request payload. An attacker with Web Admin privileges can set this quantity to an extremely low value (e.g., 0 or 1), causing the system to truncate existing logs to that size. This effectively deletes historical log data, erasing evidence of prior attacks or unauthorized actions.

The root cause is CWE-1284: Improper Validation of Specified Quantity in Input. The server does not enforce a minimum value for the quantity parameter, nor does it validate that the requested quantity is within a reasonable range. This allows an attacker to arbitrarily reduce the log size, discarding older entries.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

@app.route('/logsettings', methods=['POST'])
def update_log_settings():
    quantity = request.form.get('quantity')
    # No validation of quantity value
    set_log_max_entries(int(quantity))
    return "Settings updated"

Patched Code (Conceptual):

@app.route('/logsettings', methods=['POST'])
def update_log_settings():
    quantity = request.form.get('quantity')
    # Validate quantity is within acceptable range
    if quantity is None or not quantity.isdigit():
        return "Invalid quantity", 400
    qty = int(quantity)
    if qty < 100 or qty > 10000:
        return "Quantity out of range", 400
    set_log_max_entries(qty)
    return "Settings updated"

The patched version enforces a minimum and maximum value for the quantity parameter, preventing log truncation below a safe threshold.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Access to a Schneider Electric device with Web Admin credentials.
• Network connectivity to the device’s web interface.

Steps:

1. Authenticate as a Web Admin user.
2. Send a crafted POST request to /logsettings with a low quantity value:

   POST /logsettings HTTP/1.1
   Host: target-device
   Content-Type: application/x-www-form-urlencoded
   Cookie: session=valid_admin_session
   
   quantity=0
   

3. The server truncates all logs to 0 entries, effectively wiping the log history.
4. Perform malicious actions without leaving a trace.

Note: No public exploit code is available. This is a conceptual attack.

Blue Team (Defense & Detection)

Detection:

• Monitor for POST requests to /logsettings with abnormally low quantity values.
• Alert on any change to log settings that reduces the maximum log size below a baseline threshold.
• Enable audit logging for configuration changes (if supported).

Mitigation:

• Apply the vendor patch immediately.
• Restrict Web Admin access to trusted users only.
• Implement network segmentation to limit exposure of the web interface.
• Use a SIEM to correlate log truncation events with other suspicious activity.

Indicators of Compromise (IOCs)

• Network: POST requests to /logsettings with quantity parameter set to a value less than 100.
• Logs: Sudden drop in log entry count or missing log entries for a specific time range.
• System: Event log showing configuration change to log retention settings.

Detection Engineering

YARA Rule

rule CVE_2026_2403_LogTruncation {
    meta:
        description = "Detects POST requests to /logsettings with low quantity values"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2026-2403"
    strings:
        $post_method = "POST"
        $logsettings = "/logsettings"
        $quantity_param = "quantity="
        $low_value = /quantity=[0-9]{1,2}/
    condition:
        $post_method and $logsettings and $quantity_param and $low_value
}

Sigma Rule

title: CVE-2026-2403 - Log Truncation via /logsettings
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to truncate logs by setting a low quantity value in POST /logsettings
author: Valters IT
logsource:
    category: webserver
    product: schneider_electric
detection:
    selection:
        http.method: 'POST'
        http.url: '/logsettings'
        http.body|contains: 'quantity='
    condition: selection and (http.body|re: 'quantity=[0-9]{1,2}')
falsepositives:
    - Legitimate configuration changes with low values (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-2403 - Log Truncation Attempt"; flow:to_server; http.method; content:"POST"; http.uri; content:"/logsettings"; http.request_body; content:"quantity="; pcre:"/quantity=[0-9]{1,2}/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Apply Vendor Patch: Update the Schneider Electric device firmware to the latest version that includes the fix for CVE-2026-2403.
2. Configuration Hardening: If patching is not immediately possible, restrict access to the /logsettings endpoint using firewall rules or web application firewall (WAF) policies.
3. Access Control: Limit Web Admin privileges to only essential personnel. Use multi-factor authentication where possible.
4. Log Monitoring: Implement real-time monitoring for changes to log settings. Alert on any reduction in log size.
5. Backup Logs: Regularly export logs to an external, immutable storage system to prevent tampering.

Valters IT
DevSecOps & Cyber Threat Intelligence

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