Fastify Vulnerable to DoS via Unbounded Memory Allocation in sendWebStream

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

3.7 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2026-25224: 0.55% estimated exploitation activity in the next 30 days; percentile 45.83 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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

Published by the source

2 Feb 2026, 22:25 UTC

Last modified by the source

4 Feb 2026, 18:08 UTC

Source last checked

26 Oct 2026, 12:42 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mrq3-vjjr-p77c

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-mrq3-vjjr-p77c

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# Patch Next advisory brief: CVE-2026-25224

Advisory: Fastify Vulnerable to DoS via Unbounded Memory Allocation in sendWebStream
IDs: CVE-2026-25224, GHSA-mrq3-vjjr-p77c
Record: https://patchnext.com/advisories/cve-2026-25224 (revision 2, source checked 26 Oct 2026, 12:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fastify 5.7.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm fastify: affected <= 5.7.2; fixed in 5.7.3

## Suggested inspection (read-only)
- `npm ls fastify --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on fastify.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-mrq3-vjjr-p77c (OSV record GHSA-mrq3-vjjr-p77c lists affected ranges: npm fastify >=0 <5.7.3 (fixed))
- Verified: https://github.com/advisories/GHSA-mrq3-vjjr-p77c (GitHub-reviewed advisory GHSA-mrq3-vjjr-p77c lists affected ranges: npm fastify >=0 <=5.7.2)

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