Svelte devalue is a JavaScript library that serializes values into strings when JSON.stringify isn't sufficient for the job. In versions 5.1.0 through 5.9.2, stringify and uneval functions serialize a typed array by emitting its entire backing ArrayBuffer rather than only the view, so serializing a Node Buffer, whose backing store is a process-wide shared pool, discloses up to 64 KB of unrelated process memory, including bytes from other in-flight requests. In a server-side-rendered framework such as SvelteKit or Nuxt, a public page whose load() returns a small Buffer, or that reads a small file, can therefore ship another user's request body or Authorization header in its HTML without authentication. Because this occurs during serialization, it fires on every such render and is not mitigated by the parse/unflatten prototype-pollution and denial-of-service guards, which only apply when parsing untrusted input. As a workaround, convert Node Buffer objects to Uint8Array before serialization. This issue has been fixed in version 5.9.3.

Affected: npm: devalue

### Impact

`stringify` and `uneval` serialize a typed array by emitting its backing `ArrayBuffer`, not just the view. In the case of a Node `Buffer` object, the backing buffer is a process-wide shared pool, meaning unrelated memory can be serialized into a response that is then sent to the client. For a Node `Buffer` the backing store is Node's **process-wide shared pool**, so serializing a small `Buffer` copies up to 64 KB of unrelated process memory — including bytes from other in-flight requests — into the output. In an SSR framework (SvelteKit, Nuxt) a public page whose `load()` returns a 2-byte `Buffer`, or a small file read with `readFileSync`, ships another user's request body / `Authorization` header in its HTML. Unauthenticated, silent, ~43,000× amplification.

This is serialization-side, so the `parse`/`unflatten` prototype-pollution and DoS guards do not apply — it fires on every SSR render, not only when parsing untrusted input.

### Workarounds

Convert Node `Buffer` objects to `Uint8Array`:

```diff payload = { - buffer + buffer: new Uint8Array(buffer) } ```