Bun arrived promising to be a faster, more ergonomic alternative to Node.js. It delivers on performance through aggressive native implementation of JavaScript APIs, using Zig and JavaScriptCore instead of V8. But performance optimizations sometimes trade off against security properties, and Bun's relative youth means its security model is less battle-tested than Node.js's.
This is not an argument against using Bun. It is an argument for understanding where the security boundaries are.
Architecture and Security Implications
Bun replaces Node.js's V8 engine with WebKit's JavaScriptCore (JSC). V8 and JSC have different security track records and different vulnerability surfaces. V8 has been the target of extensive security research due to Chrome's bug bounty program, resulting in a well-hardened engine with a large body of discovered and fixed vulnerabilities. JSC has a smaller security research community but benefits from WebKit's security work for Safari.
Much of Bun's performance comes from implementing JavaScript APIs in native Zig code rather than JavaScript. The HTTP server, file I/O, and bundler are all native implementations. This means bugs in these implementations are native code bugs -- potentially memory safety issues -- rather than JavaScript logic errors.
Zig is not a memory-safe language. It provides more safety features than C (no undefined behavior in debug mode, safety checks for integer overflow and null pointers) but does not offer the compile-time memory safety guarantees of Rust. A memory corruption bug in Bun's native code could be more exploitable than the equivalent bug in a pure JavaScript implementation.
Package Management Security
Bun includes a built-in package manager that is compatible with npm's registry and package.json. It uses bun.lockb (a binary lockfile) instead of package-lock.json.
Key security considerations:
Lifecycle scripts. Bun supports npm lifecycle scripts (preinstall, postinstall, etc.) but disables them by default for packages installed from the registry. This is a security improvement over npm, which runs lifecycle scripts by default. However, lifecycle scripts for direct dependencies are still executed, and bun install --trust enables them for all packages.
Binary lockfile. The bun.lockb file is a binary format that is not human-readable. While this improves parsing performance, it makes lockfile auditing harder. You cannot easily diff two lockfile versions to see what changed. Bun provides bun bun.lockb to generate a human-readable representation, but this is an extra step.
Registry compatibility. Bun uses the npm registry by default and supports private registries. The same supply chain risks that affect npm packages affect Bun projects: typosquatting, account compromise, dependency confusion.
Missing Security Features
As of the current version, Bun lacks several security features present in Node.js or Deno:
No permission model. Unlike Deno, Bun does not restrict what code can do at runtime. A Bun process has full access to the filesystem, network, and environment, similar to Node.js. There is no equivalent of Deno's --allow-read or --allow-net flags.
No policy system. Node.js has an experimental policy system for restricting module loading. Bun does not have an equivalent mechanism.
Less security research coverage. Node.js and V8 have extensive security research communities. Bun's Zig-based native code has received comparatively little independent security review.
What Bun Does Well
Default-off lifecycle scripts are a genuine security improvement. The majority of npm supply chain attacks rely on install scripts to execute malicious code during package installation. By disabling these by default, Bun makes the most common attack vector ineffective unless the developer explicitly opts in.
Built-in tooling reduces dependencies. Bun includes a bundler, test runner, and package manager. This means fewer development dependencies, which reduces the supply chain attack surface. A project that uses bun test instead of Jest eliminates Jest and its dozens of transitive dependencies.
Fast startup improves update adoption. This is an indirect security benefit. Faster build and test times reduce the friction of applying dependency updates, which makes developers more likely to keep dependencies current.
Risk Assessment
For greenfield projects with strong security requirements, evaluate Bun against your threat model:
If supply chain defense is your priority, Bun's default-off lifecycle scripts are an advantage over npm. But Deno's permission model provides stronger containment.
If runtime isolation is important, Bun does not provide it. Consider Deno or complement Bun with OS-level sandboxing.
If your application processes untrusted input through Bun's native APIs (HTTP parsing, file I/O), you are trusting Zig code that has had less security scrutiny than Node.js's equivalent C++ code.
If you are migrating from Node.js, the npm compatibility means your existing dependency risks carry over. Bun does not magically make existing npm packages safer.
Deployment Hardening
Since Bun lacks a built-in permission model, use OS-level mechanisms to restrict what the Bun process can do:
Run under a dedicated user with minimal filesystem permissions. Use Linux capabilities to drop privileges (CAP_NET_BIND_SERVICE instead of root). Apply seccomp profiles to restrict system calls. Use container isolation with minimal base images.
These are the same hardening measures you would apply to Node.js, but they are more important for Bun because there is no runtime-level permission system to fall back on.
How Safeguard.sh Helps
Safeguard.sh provides dependency vulnerability monitoring for Bun projects, scanning your bun.lockb dependencies against known vulnerability databases. Since Bun uses npm-compatible packages, Safeguard.sh leverages its existing npm advisory coverage to protect your Bun projects. It generates SBOMs capturing your full dependency tree and alerts you when packages in your project are affected by new vulnerabilities -- giving you the supply chain visibility that Bun's built-in tooling does not yet provide.