What is the CVSS score of EUVD-2026-59757?

EUVD-2026-59757 has a CVSS 3.1 base score of 8.1 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.2%.

Which versions of @fastify/jwt are affected by EUVD-2026-59757?

A vulnerability in @fastify/jwt before version 10.2.2 allows authenticated users to bypass authorization controls when applications implement separate security keys for different roles.. A patch is available.

How to fix or mitigate EUVD-2026-59757?

Within 24 hours, inventory all applications using @fastify/jwt and identify those implementing separate security keys for user and administrator roles. Alert development teams to this authorization risk. Within 7 days, deploy version 10.2.2 or later across all affected applications-the vendor has released this patch and it should be prioritized. Within 30 days, audit JWT token validation configurations to ensure separate role-based keys are properly enforced, and review access logs from the vulnerability window for any evidence of unauthorized administrative access attempts.

@fastify/jwt EUVD-2026-59757

| CVE-2026-18500 HIGH

Improper Verification of Cryptographic Signature (CWE-347)

2026-08-15 ce714d77-add3-4f53-aff5-83d477b104bb

Information Disclosure Jwt Attack Fastify Fastify Jwt

8.1

CVSS 3.1 · Vendor: ce714d77-add3-4f53-aff5-83d477b104bb

Severity by source

Vendor (ce714d77-add3-4f53-aff5-83d477b104bb) PRIMARY

8.1 HIGH

AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

vuln.today AI

8.1 HIGH

Network-exploitable by any authenticated token holder (PR:L); AC:L because no special conditions beyond targeting a multi-key route; no availability impact applies.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (ce714d77-add3-4f53-aff5-83d477b104bb).

CVSS VectorVendor: ce714d77-add3-4f53-aff5-83d477b104bb

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

Aug 15, 2026 - 14:31 vuln.today

Patch available

Aug 15, 2026 - 14:19 EUVD

CVE Published

Aug 15, 2026 - 14:17 cve.org

HIGH 8.1

DescriptionCVE.org

@fastify/jwt is a JSON Web Token plugin for Fastify. In versions before 10.2.2, a per-request verification key passed to request.jwtVerify({ key }) is silently overridden by the plugin's globally configured secret, because the option merge applies the global key last. Applications that use different keys for different authorization domains, for example separate user and admin keys, therefore accept a token signed with the global key on a route that explicitly requires another key. This lets an ordinary authenticated user cross a key-based trust boundary without knowing either secret. The issue is fixed in @fastify/jwt 10.2.2, where an explicit per-call key takes precedence over the global secret. Users should upgrade to 10.2.2.

AnalysisAI

Key-based authorization bypass in @fastify/jwt before 10.2.2 permits any low-privileged authenticated user holding a token signed by the application's global secret to access routes explicitly restricted to a separate per-request key, silently crossing a cryptographic trust boundary. Applications implementing multi-domain JWT authorization - for example, separating user and admin token verification keys - are specifically at risk, as the plugin's option merge incorrectly applies the global key last, overriding the developer-supplied per-request key. No public exploit code has been identified and the vulnerability is not listed in the CISA KEV catalog, but the fix is available in version 10.2.2 and the attack path is mechanically straightforward for any authenticated user.

Technical ContextAI

The @fastify/jwt plugin (EUVD-2026-59757) provides JWT authentication middleware for the Fastify Node.js web framework. Its request.jwtVerify() method accepts an optional key parameter intended to override the globally configured secret for per-route trust domain separation. Due to incorrect option merge ordering - the global secret is applied last rather than first - any developer-supplied per-request key is silently overwritten before signature verification occurs. This maps to CWE-347 (Improper Verification of Cryptographic Signature): the HMAC or RSA signature is verified correctly, but against the wrong key, causing the cryptographic check to pass with an unintended secret. The affected package covers all releases from 0 up to but not including 10.2.2, as documented in the EUVD affected version range '@fastify/jwt 0 < 10.2.2'.

RemediationAI

Upgrade @fastify/jwt to version 10.2.2, the confirmed patched release per the vendor security advisory at https://github.com/fastify/fastify-jwt/security/advisories/GHSA-j4cx-787j-xjqg. In 10.2.2, an explicit per-call key correctly takes precedence over the global secret, restoring the intended trust domain isolation. For teams unable to upgrade immediately, a compensating control is to restructure the application to use separate registered Fastify plugin instances - each with its own globally configured secret - rather than relying on per-request key overrides; this eliminates the vulnerable code path but requires application refactoring and adds deployment complexity. There is no configuration-only workaround that fully mitigates the vulnerability without code changes. Additional security advisory details are available at https://cna.openjsf.org/security-advisories.html.