GHSA-g3jj-5cmm-3hxx: fast-jwt (CVE-2026-107724)

Package	Ecosystem	Affected	Fixed in
fast-jwt	npm	>=6.2.4, <6.3.0	6.3.0

Machine-written summary

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

Fast-jwt versions 6.2.4 up to but not including 6.3.0 treat a raw serialized public JWK JSON string, passed as the verifier key, as an HMAC secret when HS256 is allowed or inferred. An attacker who knows that same public JSON text can use it as the HMAC key to forge HS256 tokens that the library accepts, which can lead to authentication or authorization bypass through forged claims. Upgrade to fast-jwt 6.3.0 or later.

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
7.4	High	3.1	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0028, the 20th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 13:33 UTC First seen by agentprime
31 Oct 2026, 13:33 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.