# Fastify v5.8.3

- Product: Fastify (https://whatsnew.fyi/product/fastify)
- Vendor: Fastify
- Date: 2026-03-23
- Version: v5.8.3
- Original notes: https://github.com/fastify/fastify/releases/tag/v5.8.3
- Permalink: https://whatsnew.fyi/product/fastify/releases/v5.8.3

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **security** — Fix CVE-2026-3635
- **changed** — Allow port to be null in request type definition

##### ⚠️ Security Release

This fixes CVE CVE-2026-3635 https://github.com/fastify/fastify/security/advisories/GHSA-444r-cwp2-x5xf.

##### What's Changed
* docs(readme): add @Tony133 to plugin team by @Tony133 in https://github.com/fastify/fastify/pull/6565
* Updated Plugins-Guide.md; Changed "fastify" to "instance" during plugin registration to showcase that it's added as a child by @kyrylchenko in https://github.com/fastify/fastify/pull/6566
* test: use fastify.test in test case by @climba03003 in https://github.com/fastify/fastify/pull/6568
* docs: use fastify.example in documentation by @climba03003 in https://github.com/fastify/fastify/pull/6567
* docs: add common performance degradation guidance by @maxpetrusenko in https://github.com/fastify/fastify/pull/6520
* docs(server): fix camelCase anchor links in TOC by @Deepvamja in https://github.com/fastify/fastify/pull/6530
* ci(link-checker): fix root-relative links resolution by @barba-rossa in https://github.com/fastify/fastify/pull/6535
* docs: update syntax markdown, absolute paths and links by @Tony133 in https://github.com/fastify/fastify/pull/6569
* docs: clarify content-type parser/schema mismatch is outside threat model by @mcollina in https://github.com/fastify/fastify/pull/6537
* docs: fix incorrect code examples in Reply and Request reference by @mahmoodhamdi in https://github.com/fastify/fastify/pull/6582
* docs: replace redirected npm.im http-errors link by @mcollina in https://github.com/fastify/fastify/pull/6588
* types: Allow port to be null in request type definition by @TristanBarlow in https://github.com/fastify/fastify/pull/6589
* docs: update links by @Tony133 in https://github.com/fastify/fastify/pull/6593
* ci(lock-threads): use shared lock-threads workflow by @Fdawgs in https://github.com/fastify/fastify/pull/6592

##### New Contributors
* @kyrylchenko made their first contribution in https://github.com/fastify/fastify/pull/6566
* @maxpetrusenko made their first contribution in https://github.com/fastify/fastify/pull/6520
* @Deepvamja made their first contribution in https://github.com/fastify/fastify/pull/6530
* @barba-rossa made their first contribution in https://github.com/fastify/fastify/pull/6535
* @mahmoodhamdi made their first contribution in https://github.com/fastify/fastify/pull/6582
* @TristanBarlow made their first contribution in https://github.com/fastify/fastify/pull/6589

**Full Changelog**: https://github.com/fastify/fastify/compare/v5.8.2...v5.8.3