CVE-2026-44459: Hono JWT Auth Bypass Vulnerability

CVE-2026-44459 Overview

CVE-2026-44459 affects Hono, a web application framework supporting multiple JavaScript runtimes. The vulnerability stems from improper validation of JSON Web Token (JWT) NumericDate claims in the hono/utils/jwt module. Versions prior to 4.12.18 fail to enforce specification-compliant values for the exp, nbf, and iat claims. Tokens containing malformed claim values silently bypass time-based verification checks performed by verify(). The flaw maps to CWE-1284, improper validation of specified quantity in input. Exploitation requires that the malformed token reach verify(), typically when the application itself issues such tokens or when the signing key is under attacker control. Anonymous attackers cannot exploit this issue directly.

Critical Impact

Malformed JWT NumericDate values bypass expiration and not-before checks, allowing tokens that should be rejected to pass verification when an attacker controls token issuance or signing keys.

Affected Products

• Hono framework versions prior to 4.12.18
• Applications using hono/utils/jwt for token verification
• Node.js and other JavaScript runtime deployments of Hono

Discovery Timeline

• 2026-05-13 - CVE-2026-44459 published to NVD
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2026-44459

Vulnerability Analysis

The vulnerability resides in Hono's JWT utility module, which verifies token claims as part of the verify() function. The JWT specification defines exp (expiration), nbf (not before), and iat (issued at) as NumericDate values representing seconds since the Unix epoch. Hono prior to 4.12.18 does not enforce that these claims contain valid numeric values. When a non-spec-compliant value such as a non-numeric type, NaN, or otherwise malformed input appears in these fields, the time comparison logic silently skips the check. The token is then treated as valid for time-based constraints.

This weakness has limited reach. An anonymous external attacker cannot inject arbitrary claim values into a legitimately signed token. Exploitation requires either application logic that issues tokens with malformed claims or compromise of the signing key. In those scenarios, an attacker can forge tokens that never expire or that bypass nbf constraints, extending session validity beyond intended limits.

Root Cause

The root cause is missing type and value validation against the JWT NumericDate specification (RFC 7519). The verification routine assumes claim values are numeric without enforcing the constraint. Non-numeric or otherwise invalid inputs cause the comparison to evaluate in a manner that bypasses rejection logic rather than triggering an error.

Attack Vector

The attack vector is network-based but requires high privileges, since the attacker must influence token issuance or possess the signing key. A typical exploitation path involves an application that constructs JWTs with attacker-influenced claim fields. The attacker supplies malformed exp or nbf values, and the resulting token passes Hono's verify() despite violating intended time-based restrictions.

No verified public proof-of-concept exists for this issue. Refer to the Hono GitHub Security Advisory GHSA-hm8q-7f3q-5f36 for vendor details.

Detection Methods for CVE-2026-44459

Indicators of Compromise

• JWT tokens issued by the application containing non-numeric values in exp, nbf, or iat fields
• Authenticated sessions persisting beyond configured expiration windows
• Application logs showing successful verify() results for tokens with malformed time claims

Detection Strategies

• Inventory all services using Hono and identify the installed version via npm list hono or equivalent package manifests
• Audit JWT issuance code paths to confirm exp, nbf, and iat are written as integers and not as strings or computed expressions that may yield NaN
• Decode sample tokens from production traffic and validate that NumericDate claims conform to RFC 7519

Monitoring Recommendations

• Log JWT verification outcomes including claim values and reject any token whose time claims are not strictly numeric
• Alert on sessions that remain active beyond the maximum configured token lifetime
• Monitor dependency manifests for Hono versions below 4.12.18 across CI/CD pipelines

How to Mitigate CVE-2026-44459

Immediate Actions Required

• Upgrade Hono to version 4.12.18 or later in all affected applications
• Rotate JWT signing keys if there is any indication of key compromise
• Review token issuance logic to ensure exp, nbf, and iat are always emitted as numeric values

Patch Information

The issue is fixed in Hono 4.12.18. The vendor advisory is published at Hono Security Advisory GHSA-hm8q-7f3q-5f36. The fix adds validation that rejects tokens whose NumericDate claims are not specification-compliant.

Workarounds

• Add an application-level claim validator that runs before verify() and rejects tokens with non-numeric exp, nbf, or iat values
• Restrict access to JWT signing keys using a secrets manager and enforce least-privilege on key retrieval
• Avoid building JWT payloads from untrusted input that could influence the type or format of time claims

# Upgrade Hono to the patched version
npm install hono@^4.12.18

# Verify installed version
npm list hono