GHSA-hm8q-7f3q-5f36 Hono has improper validation of NumericDate claims (exp, nbf, iat) in JWT verify()

• npm hono: < 4.12.18 → fixed in 4.12.18

Summary Improper validation of the JWT NumericDate claims `exp`, `nbf`, and `iat` in `hono/utils/jwt` allows tokens with non-spec-compliant claim values to silently bypass time-based checks. This issue is not exploitable by an anonymous attacker; it only manifests when a malformed claim value reaches `verify()` — typically when the application itself issues such tokens, or when the signing key is otherwise under attacker control. Details The validation routine combined option, presence, and threshold checks in a single short-circuiting expression, so several classes of malformed values were silently skipped instead of rejected: • A falsy numeric value short-circuited the presence check. • A non-finite numeric value compared as never-after-now and never-expired. • A non-numeric type produced NaN comparisons that evaluated false. This deviates from RFC 7519 §4.1.4, which defines NumericDate as a finite JSON numeric value. Impact An actor able to issue tokens accepted by the application may craft tokens whose `exp`, `nbf`, or `iat` claims silently bypass time-based enforcement. This may lead to: • Tokens treated as never expiring even with `exp` configured on the verifier. • Tokens with a future `nbf` accepted as currently valid. • Tokens with a future `iat` accepted as legitimately issued. Deployments using a well-formed token issuer and protecting the signing key are not affected.