CVE-2026-2399: Web Admin Path Traversal Vulnerability

CVE-2026-2399 Overview

A Path Traversal vulnerability (CWE-22) has been identified that allows authenticated Web Admin users to overwrite critical system files with text data. The vulnerability exists in the REST API endpoint handling the POST /REST/upssleep request, where improper validation of the request payload enables directory traversal attacks.

Critical Impact

Authenticated attackers with Web Admin privileges can manipulate the POST request payload to traverse directory paths and overwrite critical system files, potentially leading to system compromise, denial of service, or arbitrary configuration changes.

Affected Products

• Schneider Electric UPS Management Software (specific versions not disclosed)
• Products utilizing the /REST/upssleep API endpoint
• Web Admin interfaces with REST API functionality

Discovery Timeline

• 2026-04-14 - CVE CVE-2026-2399 published to NVD
• 2026-04-14 - Last updated in NVD database

Technical Details for CVE-2026-2399

Vulnerability Analysis

This Path Traversal vulnerability stems from inadequate input validation in the Web Admin interface's REST API. When processing POST /REST/upssleep requests, the application fails to properly sanitize user-supplied path components, allowing attackers to include directory traversal sequences (such as ../) in the request payload.

The vulnerability requires authentication as a Web Admin user, meaning the attack surface is limited to users who have already obtained administrative credentials. However, once authenticated, an attacker can leverage this flaw to write arbitrary text data to files outside the intended directory structure, potentially overwriting critical system configuration files, application binaries, or security-sensitive data.

The impact is significant in terms of integrity and availability, as successful exploitation could corrupt essential system files, modify security configurations, or render the target system inoperable.

Root Cause

The root cause of this vulnerability is the Improper Limitation of a Pathname to a Restricted Directory (CWE-22). The application does not adequately validate or sanitize the file path parameters within the POST /REST/upssleep request payload before performing file operations. This allows directory traversal sequences to escape the intended directory and access arbitrary locations on the file system.

Key contributing factors include:

• Lack of path canonicalization before file operations
• Missing validation against directory traversal patterns
• Insufficient access controls on file write operations
• Trust placed in authenticated user input without proper sanitization

Attack Vector

The attack requires adjacent network access and high privileges (Web Admin authentication). An attacker positioned on the same network segment with valid Web Admin credentials can craft a malicious POST /REST/upssleep request containing path traversal sequences in the payload.

The attack flow involves:

1. Authenticating to the Web Admin interface with valid credentials
2. Intercepting or crafting a POST /REST/upssleep request
3. Modifying the request payload to include path traversal sequences (e.g., ../../etc/passwd)
4. The server processes the request without proper path validation
5. Critical system files are overwritten with attacker-controlled text data

Since no verified code examples are available, organizations should refer to the Schneider Electric Security Notice for detailed technical information about the vulnerability mechanism and exploitation characteristics.

Detection Methods for CVE-2026-2399

Indicators of Compromise

• Anomalous POST /REST/upssleep requests containing path traversal sequences such as ../, ..\\, or URL-encoded variants
• Unexpected file modifications in system directories outside the application's intended scope
• Web server logs showing repeated requests to the /REST/upssleep endpoint with unusual payload sizes or patterns
• System integrity alerts indicating unauthorized changes to configuration or binary files

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block path traversal patterns in REST API requests
• Monitor authentication logs for Web Admin accounts exhibiting unusual activity patterns or making requests to the upssleep endpoint
• Deploy file integrity monitoring (FIM) on critical system files to detect unauthorized modifications
• Enable detailed logging for all REST API endpoints and analyze for traversal sequence patterns

Monitoring Recommendations

• Configure SIEM alerts for HTTP requests containing common path traversal patterns targeting /REST/upssleep
• Establish baseline behavior for Web Admin accounts and alert on deviations
• Monitor file system events for write operations to sensitive directories from web application processes
• Review audit logs regularly for administrative actions involving the affected REST endpoint

How to Mitigate CVE-2026-2399

Immediate Actions Required

• Review the Schneider Electric Security Notice SEVD-2026-104-01 for vendor-specific guidance
• Restrict network access to the Web Admin interface to trusted management networks only
• Audit Web Admin user accounts and remove unnecessary administrative privileges
• Implement network segmentation to limit adjacent network exposure

Patch Information

Schneider Electric has published security guidance in their official Security Notice (SEVD-2026-104-01). Organizations should consult the Schneider Electric Security Notice for specific patch availability, affected product versions, and remediation instructions.

Workarounds

• Implement strict network segmentation to limit access to the Web Admin interface from adjacent network segments
• Deploy a reverse proxy or web application firewall (WAF) in front of the affected service to filter malicious path traversal attempts
• Enable enhanced logging and monitoring for all REST API requests to the /REST/upssleep endpoint
• Consider temporarily disabling the affected functionality if business operations permit until a patch is applied

# Example WAF rule to block path traversal attempts (ModSecurity format)
SecRule REQUEST_URI "@contains /REST/upssleep" "chain,id:1001,phase:2,deny,status:403,log,msg:'Path Traversal Attempt Blocked'"
SecRule REQUEST_BODY "@rx \.\.\/" "t:urlDecodeUni,t:htmlEntityDecode"