CVE-2026-25551 in BarTender 2021
Summary
by MITRE • 06/04/2026
Seagull Software BarTender 2021 R1 through 12.0.1 contains an insecure deserialization vulnerability that allows low-privileged local users to escalate privileges. The DataServiceSingleton .NET Remoting endpoint is bound to localhost on TCP port 7375 via BtSystem.Service.exe, limiting the attack surface to local access only. The endpoint is configured with BinaryServerFormatterSinkProvider and TypeFilterLevel set to Full. A low-privileged local attacker can send YSoSerial.NET-generated BinaryFormatter payloads to the localhost-bound endpoint to achieve code execution as NT AUTHORITY\\SYSTEM.
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Analysis
by VulDB Data Team • 06/04/2026
The vulnerability under discussion represents a critical privilege escalation flaw within Seagull Software BarTender versions 2021 R1 through 12.0.1, demonstrating how insecure deserialization can be exploited to achieve system-level compromise. This issue resides in the DataServiceSingleton .NET Remoting endpoint that operates on localhost port 7375 through the BtSystem.Service.exe process, creating a confined attack surface that limits exploitation to local system access. The vulnerability stems from the endpoint's configuration using BinaryServerFormatterSinkProvider with TypeFilterLevel set to Full, which permits unrestricted deserialization of arbitrary .NET objects. This configuration creates a dangerous environment where untrusted data can be deserialized without proper validation, enabling attackers to craft malicious payloads that execute arbitrary code with elevated privileges. The attack vector specifically leverages YSoSerial.NET-generated BinaryFormatter payloads, which exploit the .NET framework's deserialization mechanism to execute code on the target system.
The technical exploitation of this vulnerability follows a well-established pattern within the cybersecurity landscape, aligning with common attack techniques documented in the ATT&CK framework under privilege escalation tactics. The flaw manifests as a direct consequence of insecure deserialization practices that have been classified under CWE-502, which specifically addresses deserialization of untrusted data. The endpoint's binding to localhost does not adequately mitigate the risk since local privilege escalation remains a significant concern, particularly when the service operates with elevated privileges. The TypeFilterLevel set to Full essentially disables the security restrictions that would normally prevent deserialization of dangerous object types, creating an environment where attackers can inject malicious code that executes with the privileges of the hosting service. This represents a fundamental security misconfiguration that transforms a local access point into a critical attack vector for privilege escalation.
The operational impact of this vulnerability extends beyond simple code execution, as it enables attackers to achieve complete system compromise through the escalation of privileges to NT AUTHORITY\SYSTEM. This level of access provides attackers with unrestricted control over the target system, including the ability to modify or delete files, create new user accounts, access all system resources, and potentially establish persistence mechanisms. The implications are particularly severe given that the service typically runs with elevated privileges to perform its intended functions, making the privilege escalation path particularly attractive to attackers. The vulnerability essentially provides a backdoor mechanism that bypasses normal authentication and authorization controls, allowing local attackers to gain the highest level of system access without requiring additional credentials or complex attack chains.
Mitigation strategies for this vulnerability must address the core issue of insecure deserialization within the .NET Remoting endpoint. The most effective immediate solution involves configuring the TypeFilterLevel to a more restrictive setting, specifically limiting it to Medium or High rather than Full, which would prevent the deserialization of dangerous object types. Additionally, the endpoint should be configured to use more secure serialization mechanisms such as JSON or XML serialization instead of BinaryFormatter, which is inherently unsafe for untrusted input. Organizations should also implement proper access controls and monitoring for the BtSystem.Service.exe process to detect unauthorized access attempts. The remediation approach should align with industry best practices for secure coding and configuration management, as outlined in various cybersecurity frameworks including NIST SP 800-53 and ISO 27001 standards. Regular security assessments and vulnerability scanning should be implemented to identify similar insecure deserialization patterns in other applications and services within the environment.