CVE-2026-34240: Appsup-Dart Jose

High severity, CVSS 7.5. EPSS: 0.2% chance of exploitation in the next 30 days.

JOSE is a Javascript Object Signing and Encryption (JOSE) library. Prior to version 0.3.5+1, a vulnerability in jose could allow an unauthenticated, remote attacker to forge valid JWS/JWT tokens by using a key embedded in the JOSE header (jwk). The vulnerability exists because key selection could treat header-provided jwk as a verification candidate even when that key was not present in the trusted key store. Since JOSE headers are untrusted input, an attacker could exploit this by creating a token payload, embedding an attacker-controlled public key in the header, and signing with the matching private key. Applications using affected versions for token verification are impacted. This issue has been patched in version 0.3.5+1. A workaround for this issue involves rejecting tokens where header jwk is present unless that jwk matches a key already present in the application's trusted key store.

Affected products

• Appsup-Dart Jose: before 0.3.5\+1 (fixed in 0.3.5\+1)

Published 2026-03-31. Last modified 2026-07-24.