CVE-2025-27539: Siemens Telecontrol Server Basic SQLi

CVE-2025-27539 Overview

A critical SQL injection vulnerability has been identified in Siemens TeleControl Server Basic, affecting all versions prior to V3.1.2.2. The vulnerability exists in the internally used VerifyUser method, which fails to properly sanitize user input before incorporating it into SQL queries. This flaw allows an unauthenticated remote attacker to bypass authorization controls, read from and write to the application's database, and execute arbitrary code with NT AUTHORITY\NetworkService permissions.

Critical Impact

Unauthenticated attackers can bypass authentication, manipulate database contents, and achieve remote code execution on vulnerable TeleControl Server Basic installations accessible on port 8000.

Affected Products

• Siemens TeleControl Server Basic (All versions < V3.1.2.2)

Discovery Timeline

• April 16, 2025 - CVE-2025-27539 published to NVD
• August 19, 2025 - Last updated in NVD database

Technical Details for CVE-2025-27539

Vulnerability Analysis

This SQL injection vulnerability (CWE-89) affects the authentication mechanism within Siemens TeleControl Server Basic. The VerifyUser method, responsible for user authentication operations, does not adequately validate or sanitize input parameters before constructing SQL queries. As a result, malicious SQL statements can be injected through the authentication interface.

The vulnerability is particularly severe because it targets the authentication layer itself, allowing attackers to completely bypass access controls. Successful exploitation grants attackers the ability to read sensitive data from the database, modify or delete critical records, and escalate to code execution with the privileges of the NT AUTHORITY\NetworkService account.

Root Cause

The root cause of this vulnerability is improper neutralization of special elements used in SQL commands. The VerifyUser method constructs SQL queries using unsanitized user-supplied input, allowing attackers to manipulate query logic through specially crafted input strings. This represents a classic SQL injection pattern where dynamic query construction without parameterized queries or proper input validation creates an exploitable condition.

Attack Vector

The attack requires network access to port 8000 on a system running a vulnerable version of TeleControl Server Basic. An unauthenticated attacker can send specially crafted requests to the VerifyUser endpoint containing malicious SQL payloads. The attack does not require any user interaction or prior authentication, making it highly exploitable in environments where port 8000 is accessible.

The exploitation chain follows a typical SQL injection pattern:

1. Attacker identifies a TeleControl Server Basic instance accessible on port 8000
2. Malicious SQL payload is crafted to target the VerifyUser authentication method
3. The payload bypasses authentication controls and gains database access
4. From database access, the attacker can escalate to code execution with NetworkService privileges

Detection Methods for CVE-2025-27539

Indicators of Compromise

• Unexpected or malformed authentication requests to port 8000 containing SQL syntax characters such as single quotes, double dashes, or UNION keywords
• Anomalous database queries or error messages in TeleControl Server Basic logs
• Unauthorized modifications to database records or user accounts
• Processes spawning under NT AUTHORITY\NetworkService context that are not typical for TeleControl Server operations
• Network traffic patterns showing unusual data exfiltration from systems hosting TeleControl Server Basic

Detection Strategies

• Implement network intrusion detection rules to identify SQL injection patterns in traffic destined for port 8000
• Monitor authentication logs for repeated failed login attempts followed by successful authentication from the same source
• Deploy application-layer firewalls configured to detect and block SQL injection payloads
• Enable verbose logging on TeleControl Server Basic and centralize logs for security analysis

Monitoring Recommendations

• Configure alerting for any direct access attempts to port 8000 from untrusted network segments
• Monitor for database query anomalies including unexpected SELECT, INSERT, UPDATE, or DELETE operations
• Track process creation events associated with the TeleControl Server service account
• Implement file integrity monitoring on critical TeleControl Server configuration and database files

How to Mitigate CVE-2025-27539

Immediate Actions Required

• Upgrade Siemens TeleControl Server Basic to version V3.1.2.2 or later immediately
• Restrict network access to port 8000 to only authorized and trusted systems
• Implement network segmentation to isolate industrial control systems from general network access
• Review database logs and authentication records for evidence of prior exploitation attempts

Patch Information

Siemens has released a security update addressing this vulnerability in TeleControl Server Basic version V3.1.2.2. Organizations should prioritize applying this update as the vulnerability allows unauthenticated remote code execution. Detailed patch information and download links are available in the Siemens Security Advisory SSA-443402.

Workarounds

• If immediate patching is not possible, block external network access to port 8000 using firewall rules
• Implement a Web Application Firewall (WAF) or network-based SQL injection detection in front of TeleControl Server instances
• Consider placing TeleControl Server Basic behind a VPN to restrict access to authenticated users only
• Enable additional logging and monitoring to detect exploitation attempts while awaiting patch deployment