CVE-2026-25224: 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
Other sources
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 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. This issue has been patched in version 5.7.3.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-25224?
CVE-2026-25224 is classified as a Denial of Service vulnerability.
How do I fix CVE-2026-25224?
To mitigate CVE-2026-25224, upgrade Fastify to version 5.7.3 or later.
What applications are affected by CVE-2026-25224?
Applications that return a ReadableStream via reply.send() are affected by CVE-2026-25224.
Can CVE-2026-25224 lead to server memory exhaustion?
Yes, CVE-2026-25224 can allow a remote client to exhaust server memory.
What is the nature of the attack for CVE-2026-25224?
CVE-2026-25224 can be exploited by a slow or non-reading client, resulting in resource exhaustion.