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Fastify\/accepts SerializerApplication · Fastify

CVE-2026-7768

HIGH · 7.5 CVSS v3.1 Published 2026-05-04
Fix available
A fix is available. Upgrade to 6.0.4 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
@fastify/accepts-serializer cached serializer-selection results keyed by the request Accept header without a size limit or eviction policy. A remote unauthenticated client could send many distinct but matching Accept header variants to make the cache grow unbounded, eventually exhausting the Node.js heap and crashing the process. Versions <= 6.0.3 are affected. Update to 6.0.4 or later, which bounds the cache via an LRU with a default size of 100 entries, configurable through the new cacheSize plugin option.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The @fastify/accepts-serializer plugin cached serializer-selection results keyed by the HTTP Accept header without any size limit or eviction policy. A remote unauthenticated attacker could send numerous distinct Accept header variants to cause unbounded cache growth, eventually exhausting Node.js heap memory and crashing the service.

MitigationUpdate @fastify/accepts-serializer from any version <= 6.0.3 to version 6.0.4 or later, which implements an LRU cache with a default size of 100 entries and exposes a configurable cacheSize option.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Fastify\/accepts SerializerApplication
Affected:< 6.0.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify if @fastify/accepts-serializer is installed
    Run 'npm list @fastify/accepts-serializer' or inspect package.json dependencies to see if the package is listed
    Affected if The package is present in node_modules or package.json dependencies
  2. Check the installed version
    Run 'npm list @fastify/accepts-serializer' to see the exact version number, or check the version in node_modules/@fastify/accepts-serializer/package.json
    Affected if The installed version is less than 6.0.4 (for example, 6.0.3, 6.0.2, 6.0.1, 6.0.0, or any version below 6.0.4)
  3. Verify the plugin is registered in the Fastify app
    Search the application source code for 'accepts-serializer' or 'fastify.acceptsSerializer' to confirm the plugin is being used
    Affected if The plugin code is imported and registered with a Fastify instance using fastify.register() or similar
  4. Determine if the service is network-accessible
    Check server configuration for binding address (0.0.0.0 or public IP versus 127.0.0.1) and whether authentication/authorization guards are in place before Accept header processing
    Affected if The HTTP server listens on a public or external interface (not localhost only) and accepts requests without authentication

You are affected if @fastify/accepts-serializer version below 6.0.4 is installed, the plugin is actively used in your Fastify application, and your service is accessible over the network to unauthenticated clients who can send arbitrary Accept headers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.0.4 or later
Fixed in 6.0.4
Interim mitigation

Update @fastify/accepts-serializer from any version <= 6.0.3 to version 6.0.4 or later, which implements an LRU cache with a default size of 100 entries and exposes a configurable cacheSize option.

Recommended fix High confidence

6.0.4

  1. Check the current version of @fastify/accepts-serializer in your project by reviewing package.json or running npm list @fastify/accepts-serializer
  2. Update @fastify/accepts-serializer to version 6.0.4 or later using your package manager (e.g., npm install @fastify/accepts-serializer@^6.0.4, pnpm add @fastify/accepts-serializer@^6.0.4, or yarn add @fastify/accepts-serializer@^6.0.4)
  3. Run your test suite to verify the application functions correctly after the update
  4. Optional: If a custom cache size is needed, configure the cacheSize option in your Fastify plugin registration (the default LRU cache size is 100 entries)

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Fastify\/accepts Serializer Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-7768 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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