Deno and Bun take significantly different approaches to security, reflecting their distinct design philosophies and target use cases.
Deno was designed with security as a fundamental priority, adopting a "secure by default" model. With Deno, code executing in its runtime begins with no access to the file system, network, environment variables, or subprocesses unless these permissions are explicitly granted by the developer. This permissions model is enforced at runtime via command-line flags such as `--allow-read` for file system access or `--allow-net` for network access. The goal is to limit the attack surface and prevent unauthorized resource access. Deno requires that permissions be granted explicitly and intentionally, thus encouraging careful consideration of the resources a program or its dependencies can access. This model creates a sandboxed execution environment using V8 engine capabilities coupled with Rust-based runtime interposition to strictly control I/O operations. Deno does not allow privilege escalation during runtime without explicit consent, increasing security further. Additionally, Deno's standard library is secured with best practices in mind, and the runtime isolates code execution to prevent malicious interference with other processes or the underlying system. This includes no access to critical system resources like the Windows registry or macOS keychain. Overall, Deno's approach helps developers run untrusted code with confidence and better manage dependency risks through runtime permission visibility and control.
In contrast, Bun follows a more traditional, permissive security model akin to Node.js. By default, Bun does not restrict access to system resources such as the file system or network. This facilitates easy startup and rapid development without the need to configure explicit permissions. However, this convenience comes at the cost of having a larger attack surface and less isolation for code execution. Any code or dependency can freely access files or make network requests unless developers manually implement safeguards in application logic or infrastructure. Bun inherits much of its security profile from Node.js, including shared vulnerabilities that arise from the lack of a strict permission model or sandboxing layer in the runtime. While Bun emphasizes performance and developer experience, its current absence of a permissions system or sandbox makes it more suitable for rapid prototyping and local development rather than production environments where security is critical. The Bun team has plans to develop security features and perform security audits, but as of now, Bun's security model relies heavily on the developer's responsibility and external controls rather than built-in runtime enforcement.
Key differences between Deno and Bun's security approaches include:
- Deno enforces strict, explicit runtime permissions for file, network, environment, and subprocess access, preventing unauthorized resource access by default; Bun lacks this layer of enforcement.
- Deno runs code in a sandboxed environment utilizing V8's sandboxing and Rust runtime interposition, limiting code capabilities; Bun does not implement sandboxing.
- Deno aims to prevent privilege escalation during program execution without user consent; Bun has no built-in mechanism for privilege control during runtime.
- Deno encourages good security hygiene by making runtime permissions visible and configurable by the developer, reducing risks from third-party dependencies; Bun leaves permission control to developers.
- Bun prioritizes speed, performance, and ease of use, which results in a more permissive security posture compared to Deno's security-first approach.
Deno's security model is well-suited for scenarios requiring strong isolation, multi-tenant environments, or handling sensitive data. By contrast, Bun's security approach is more developer-friendly for rapid development but less restrictive and secure by default. This contrast outlines a fundamental trade-off between security and developer convenience or performance between the two runtimes.
In summary, Deno stands out as a JavaScript and TypeScript runtime environment with a comprehensive security architecture based on explicit permission granting, sandboxing, and controlled access to resources. Bun adopts a permissive security model similar to Node.js, focusing on speed and ease at the expense of built-in security controls, which leaves security management to the developer and external infrastructure. This makes Deno preferable for production and security-sensitive applications, while Bun is better for fast prototyping and performance-centric workflows.
This detailed comparison highlights the core distinctions in security philosophy and mechanisms between Bun and Deno.