CVE-2025-15559: NesterSoft WorkTime RCE Vulnerability

CVE-2025-15559 Overview

CVE-2025-15559 is a critical OS command injection vulnerability (CWE-78) affecting NesterSoft WorkTime server software. An unauthenticated attacker can inject arbitrary operating system commands when calling a server API endpoint. The vulnerability exists in the guid parameter of the server API call used to generate and download the WorkTime client from the WorkTime server.

Critical Impact

Successful exploitation allows an attacker to execute arbitrary commands on the WorkTime server as NT Authority\SYSTEM with the highest privileges, enabling complete server takeover and access to sensitive data.

Affected Products

• NesterSoft WorkTime Server (versions not specified)

Discovery Timeline

• 2026-02-19 - CVE-2025-15559 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2025-15559

Vulnerability Analysis

This command injection vulnerability allows unauthenticated attackers to compromise the entire WorkTime server infrastructure. The flaw exists in an API endpoint responsible for generating and delivering the WorkTime client application. When processing requests to this endpoint, user-supplied input in the guid parameter is passed directly to operating system command execution functions without proper sanitization or validation.

The vulnerability is particularly severe because it requires no authentication, meaning any attacker with network access to the WorkTime server can exploit it. Furthermore, the commands execute in the context of NT Authority\SYSTEM, which is the highest privilege level on Windows systems.

Root Cause

The root cause is improper neutralization of special elements used in an OS command (CWE-78). The server-side code fails to sanitize user input in the guid parameter before incorporating it into system commands. This allows attackers to break out of the intended command context and inject additional commands that will be executed by the underlying operating system.

Attack Vector

The attack is executed through the WorkTime server API endpoint used for client generation and download. An attacker sends a specially crafted HTTP request to this endpoint with malicious OS commands embedded in the guid parameter. The server processes this parameter without adequate input validation, resulting in the injected commands being executed with SYSTEM-level privileges.

Typical exploitation involves appending command separators (such as &, |, or ; on Windows) followed by arbitrary commands. This could include downloading and executing malware, creating new administrator accounts, exfiltrating sensitive data, or establishing persistent backdoor access to the server.

For detailed technical information about this vulnerability, refer to the SEC Consult security advisory.

Detection Methods for CVE-2025-15559

Indicators of Compromise

• Unusual process spawning from the WorkTime server process, especially command interpreters like cmd.exe or powershell.exe
• Unexpected network connections originating from the WorkTime server to external IP addresses
• Suspicious entries in Windows Event Logs showing SYSTEM-level command execution
• Anomalous HTTP requests to the WorkTime client generation API with unusual guid parameter values containing shell metacharacters

Detection Strategies

• Monitor HTTP traffic to the WorkTime server for requests containing command injection patterns such as &, |, &&, ||, ;, or backticks in the guid parameter
• Implement Web Application Firewall (WAF) rules to detect and block OS command injection attempts targeting the vulnerable endpoint
• Configure endpoint detection and response (EDR) solutions to alert on unexpected child processes spawned by the WorkTime server application

Monitoring Recommendations

• Enable detailed logging on the WorkTime server to capture all API requests and their parameters
• Set up SIEM alerts for patterns indicative of command injection attempts in web server logs
• Monitor for privilege escalation activities and unusual SYSTEM-level process creation events

How to Mitigate CVE-2025-15559

Immediate Actions Required

• Restrict network access to the WorkTime server, limiting connections to trusted IP ranges only
• Place the WorkTime server behind a properly configured Web Application Firewall with command injection rules enabled
• Monitor the WorkTime server for any signs of compromise while awaiting an official patch
• Consider temporarily disabling the vulnerable client generation API endpoint if operationally feasible

Patch Information

No official patch information is currently available in the NVD database. Organizations should monitor the SEC Consult security advisory and the NesterSoft vendor website for updates regarding security patches or updated software versions.

Workarounds

• Implement network segmentation to isolate the WorkTime server from untrusted networks
• Deploy a reverse proxy or WAF in front of the WorkTime server with strict input validation rules for the guid parameter
• Apply the principle of least privilege by running the WorkTime service with reduced permissions where possible, though this may not be fully effective given the SYSTEM-level execution context
• Enable comprehensive audit logging and establish real-time monitoring of the WorkTime server

# Example Windows Firewall rule to restrict access to WorkTime server port
# Replace 8080 with the actual WorkTime server port and trusted IP ranges
netsh advfirewall firewall add rule name="Restrict WorkTime Server Access" dir=in action=allow protocol=tcp localport=8080 remoteip=192.168.1.0/24
netsh advfirewall firewall add rule name="Block WorkTime Public Access" dir=in action=block protocol=tcp localport=8080