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Low

Fastify Vulnerable to DoS via Unbounded Memory Allocation in sendWebStream

  • Disclosed: 02.02.2026
  • Updated: 11.10.2026 10:22

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

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
npm package fastify < 5.7.3 5.7.3

References

CVSS score 3.7/10
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness (CWE)
CWE-770
Platform
npm
Package
fastify
Disclosed
02.02.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-mrq3-vjjr-p77c - CC BY 4.0

Vulnerability history: fastify

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (16) in the archive
Total entries
16
First → latest
07.2018 09.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • High 8
  • Medium 7
  • Low 1

Disclosures per year

Severity:
  1. fastify vulnerable to request body replacement via an async validation result collision
    High · 8.1 CVE-2026-84504 < 5.12.2 5.12.2
  2. fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers
    High · 7.5 CVE-2026-76169 >= 4.0.0, < 5.12.2 5.12.2
  3. fastify vulnerable to request validation bypass via skipped boolean false schemas
    High · 7.5 CVE-2026-84469 < 5.12.2 5.12.2
  4. fastify vulnerable to header validation bypass via incomplete schema case normalization
    High · 7.5 CVE-2026-84428 < 5.12.2 5.12.2
  5. Fastify Vulnerable to DoS via Unbounded Memory Allocation in sendWebStream this entry
    Low · 3.7 CVE-2026-25224 < 5.7.3 5.7.3
  6. Fastify's Content-Type header tab character allows body validation bypass
    High · 7.5 CVE-2026-25223 < 5.7.2 5.7.2
  7. Fastify vulnerable to invalid content-type parsing, which could lead to validation bypass
    High · 7.5 CVE-2025-32442 >= 5.0.0, < 5.3.2, >= 4.29.0, < 4.29.1 5.3.2, 4.29.1
  8. fastify vulnerable to denial of service via malicious Content-Type
    High · 7.5 CVE-2022-39288 >= 4.0.0, < 4.8.1 4.8.1
  9. Denial of Service vulnerability with large JSON payloads in fastify
    High · 7.5 CVE-2018-3711 < 0.38.0 0.38.0

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