GHSA-9q9j-q6p8-xq58: fastify (CVE-2026-84428)

Package	Ecosystem	Affected	Fixed in
fastify	npm	<5.12.2	5.12.2

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

GHSA-9q9j-q6p8-xq58 affects the npm package fastify before 5.12.2. Header schemas that use JSON Schema `dependencies` with mixed-case header names are not normalized correctly, so a dependency between headers can be silently skipped. An unauthenticated remote client can send the header that activates a privileged path while omitting the dependent header, bypassing that schema-enforced control. Upgrade to fastify 5.12.2 or later, which also appears in 6.0.0; if upgrading is not possible, use lowercase header-schema names or enforce the check in an onRequest or preValidation hook.

Written 31 Oct 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
7.5	High	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N	CNA (openjs)

CISA KEV Not listed.
EPSS 0.0052, the 44th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 13:34 UTC First seen by agentprime
31 Oct 2026, 13:34 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.