CVE-2026-25224 is a low-severity (CVSS 3.7) CWE-770 vulnerability in fastify. A fix is available for fastify — see the affected versions and patch details below.
Fastify Vulnerable to DoS via Unbounded Memory Allocation in sendWebStream
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-25224.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
fastifynpmDescription
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fastify | all versions | 5.7.3npm install fastify@5.7.3 |
Affected Products
fastifyfastifyDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fastify to 5.7.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-25224 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
LOW. A denial-of-service flaw exists in Fastify's Web Streams response handling. This issue can lead to unbounded buffering and memory exhaustion when a remote client sends a slow or non-reading request to an application that uses `reply.send()` with a `ReadableStream` or `Response` with a Web Stream body. Red Hat…
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for CVE-2026-25224 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-25224 in your dependencies?
Find it across npm, including transitive dependencies.