GHSA-5hjw-83fp-phq9: fast-jwt (CVE-2026-107723)

Package	Ecosystem	Affected	Fixed in
fast-jwt	npm	<6.3.0	6.3.0

Machine-written summary

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

The fast-jwt npm package, versions before 6.3.0, has a flaw in createVerifier: when a JWT with a valid signature carries a JSON array as its payload instead of an object, the verifier skips all configured claim checks (exp, nbf, iss, aud, sub, jti, nonce) and reports success after checking only the signature. An attacker needs a token signed with a key the verifier trusts, which might be held by another party or an issuer that accepts attacker-controlled payload content. Upgrade to fast-jwt 6.3.0 or later, which fixes the issue.

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

CISA KEV Not listed.
EPSS 0.0046, the 39th percentile, on 5 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.