CVE-2026-25224Network attack vector

Memory exhaustion via ignored Web Stream backpressure

Published Feb 3, 2026 · Updated Feb 3, 2026

Denial of service in Fastify before 5.7.3 allows remote attackers to crash Node.js servers through slow Web Stream responses. sendWebStream ignored a false return from res.write() and continued reading chunks instead of waiting for the response drain event, causing unbounded buffering. The application must send a ReadableStream or a Response with a Web Stream body through reply.send(); a slow or non-reading client can then exhaust process memory.

CVSS severity3.7
Low
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Fastify before 5.7.3 allows remote attackers to crash Node.js servers through slow Web Stream responses. sendWebStream ignored a false return from res.write() and continued reading chunks instead of waiting for the response drain event, causing unbounded buffering. The application must send a ReadableStream or a Response with a Web Stream body through reply.send(); a slow or non-reading client can then exhaust process memory.

The record

CVE
CVE-2026-25224
Published
Feb 3, 2026
Updated
Feb 3, 2026
Vendor
Fastify
Product
Fastify
Classifications
CWE-770, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 5.7.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Fastify · Fastifyversion=< 5.7.3

Published CVSS scores

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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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