Fastify up to 5.7.2 reply.send allocation of resources

Summaryinfo

A vulnerability categorized as problematic has been discovered in Fastify up to 5.7.2. Impacted is the function reply.send. The manipulation results in allocation of resources. This vulnerability is cataloged as CVE-2026-25224. The attack may be launched remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Fastify up to 5.7.2. It has been classified as problematic. Affected is the function reply.send. The manipulation with an unknown input leads to a allocation of resources vulnerability. CWE is classifying the issue as CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. This is going to have an impact on availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-25224 since 01/30/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 5.7.3 eliminates this vulnerability. Applying the patch eb11156396f6a5fedaceed0140aed2b7f026be37 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-5158). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Name

• Fastify

Version

• 5.7.0
• 5.7.1
• 5.7.2

License

• open-source

Website

• Product: https://github.com/fastify/fastify/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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