Fastify Vulnerable to DoS via Unbounded Memory Allocation in sendWebStream
### Impact A Denial of Service vulnerability in Fastify’s Web Streams response handling can allow a remote client to exhaust server memory. Applications that return a `ReadableStream` (or `Response` with a Web Stream body) via `reply.send()` are impacted. A slow or non-reading client can trigger unbounded buffering when backpressure is ignored, leading to process crashes or severe degradation. ### Patches The issue is fixed in Fastify 5.7.3. Users should upgrade to 5.7.3 or later. ### Workarounds Avoid sending Web Streams from Fastify responses (e.g., `ReadableStream` or `Response` bodies). Use Node.js streams (`stream.Readable`) or buffered payloads instead until the project can upgrade. ### References - https://hackerone.com/reports/3524779
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-25224US | — | — | ||
Fastify is a fast and low overhead web framework, for Node.js. Prior to version 5.7.3, a denial-of-service vulnerability in Fastify’s Web Streams response handling can allow a remo… | ||||
references
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