# CVE-2026-7768: Fastify @fastify/accepts-serializer denial of service via unbounded cache growth

Source: https://junglewise.ai/threats/cve-2026-7768-fastify-fastify-accepts-serializer-denial-of-service-via-unbounded  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-04. Updated: 2026-05-29  
License: CC BY 4.0 with a link back

CVE-2026-7768 · Severity: high · CVSS 7.5 · Published 2026-05-04

A vulnerability in a Fastify plugin used for handling web request formats could allow an attacker to crash the server. By sending a large number of specially crafted web requests, an attacker can force the server to use up all its available memory. This results in a denial-of-service condition, making the application unavailable to legitimate users.

Vendors: [Fastify](https://junglewise.ai/threats/vendors/fastify), [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-7768 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-7768 being exploited in the wild.

**How severe is CVE-2026-7768?** High severity, with a CVSS score of 7.5, published 4 May 2026.

**Which products and versions are affected?** Fastify Accepts-Serializer <= 6.0.3; @fastify/accepts-serializer (npm) SEMVER:introduced=0,fixed=6.0.4.

**Is there a fix for CVE-2026-7768?** Yes. @fastify/accepts-serializer (npm): upgrade to 6.0.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-7768 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-7768?** Check whether you run Fastify Accepts-Serializer or @fastify/accepts-serializer (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- @fastify/accepts-serializer (npm): upgrade to 6.0.4 or later

  ```sh
  npm install @fastify/accepts-serializer@6.0.4
  ```


## Technical details

The @fastify/accepts-serializer plugin fails to implement a size limit or eviction policy for its internal cache used to store serializer-selection results. The cache is keyed by the 'Accept' request header; consequently, a remote unauthenticated attacker can send numerous requests with unique Accept header variants to cause unbounded memory consumption. This leads to Node.js heap exhaustion and a process crash (CWE-770). The issue is resolved in version 6.0.4, which introduces a Least Recently Used (LRU) cache with a default limit of 100 entries.

## Affected products

- Fastify @fastify/accepts-serializer <= 6.0.3

## Identifiers

- CVE-2026-7768
- GHSA-qxhc-wx3p-2wmg

## Timeline

- 2026-05-04: disclosed
- 2026-05-04: advisory
- 2026-05-04: patched

## References

- [https://cna.openjsf.org/security-advisories.html](https://cna.openjsf.org/security-advisories.html)
- [https://github.com/fastify/fastify-accepts-serializer/security/advisories/GHSA-qxhc-wx3p-2wmg](https://github.com/fastify/fastify-accepts-serializer/security/advisories/GHSA-qxhc-wx3p-2wmg)