STunnel
Encryption software
Confidentiality software
- Features
- Ease of use
- Ease of management
- Quality of support
- Affordability
- Market presence
Take the quiz to check if STunnel and its alternatives fit your requirements.
$740 one-time
Free Trial unavailable
Free version
Small
Medium
Large
- Information technology and software
- Professional services (engineering, legal, consulting, etc.)
- Banking and insurance
What is STunnel
stunnel is an open-source TLS/SSL tunneling proxy that adds transport encryption to existing client/server applications without requiring changes to the application code. It is commonly used by system administrators and developers to wrap legacy or plaintext services (for example, SMTP, IMAP, LDAP, database connections) with TLS, or to terminate TLS and forward traffic internally. The software runs as a standalone daemon and can operate in client or server mode, relying on OpenSSL for cryptographic functions. It is typically deployed as an infrastructure component rather than an end-user confidentiality application.
Adds TLS without app changes
stunnel can encrypt traffic for applications that do not natively support TLS by placing a proxy in front of the service. This makes it useful for legacy systems and third-party software where source code changes are not feasible. It supports both client-side and server-side tunneling, enabling flexible placement in network architectures. This focus on transport wrapping differentiates it from platforms centered on data governance or end-user file protection.
Mature, widely portable daemon
stunnel has a long operating history and is available across common Unix/Linux distributions and Windows. It runs as a lightweight service with straightforward process supervision and logging integration. The configuration model is file-based and works well with standard infrastructure automation patterns. For teams that prefer minimal dependencies, it can be simpler to deploy than broader confidentiality suites.
Leverages standard TLS ecosystem
stunnel uses OpenSSL and standard X.509 certificates, allowing integration with existing PKI, certificate rotation processes, and common cipher policy controls. It supports mutual TLS (client certificates) for stronger endpoint authentication in addition to encryption. This standards-based approach helps interoperability with diverse clients and servers. It also allows security teams to align settings with organizational TLS baselines.
Not a data protection platform
stunnel encrypts data in transit but does not provide data classification, tokenization, field-level encryption, or policy-based access controls. It does not address at-rest confidentiality, rights management, or privacy workflows that some confidentiality products focus on. Organizations needing centralized governance, auditing across datasets, or application-layer controls typically require additional tooling. As a result, it is best viewed as a building block rather than a complete confidentiality solution.
Operational complexity and risk
Correct configuration requires TLS expertise, including certificate management, protocol/cipher selection, and secure key handling. Misconfiguration (for example, weak ciphers, improper verification, or poor key storage) can reduce security despite using TLS. Ongoing operations include certificate renewal, monitoring, and incident response for exposed endpoints. These tasks can be heavier than managed services that abstract certificate lifecycle management.
Limited enterprise management features
stunnel does not include a centralized management console, role-based administration, or built-in compliance reporting. Scaling to many endpoints typically relies on external configuration management and monitoring systems. Troubleshooting can be more manual, especially in heterogeneous environments. Enterprises may need to build supporting processes to achieve consistent policy enforcement and visibility.
Plan & Pricing
| Plan | Price | Key features & notes |
|---|---|---|
| Community / Software (GPL) | Free | Stunnel distributed under GNU GPL v2 (or later) with OpenSSL exception; free to download and use. |
| Basic Support Plan | $740 (USD) or | Up to 10 hours of email support to be used within 3 months; 2 working days maximum response time. |
| Commercial Support (negotiated) | Custom / Contact sales | Several levels of response time up to 24/7/365 helpline; fees negotiated individually based on number of stunnel users and required service level. |
| Commercial Licenses | Custom / Contact sales | Custom licensing for distributing modified versions without sharing source or linking with GPL-incompatible code; contact stunnel for negotiation. |
