Vulnerability in Appsup-Dart Jose
CVE-2026-34240
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.002 (8.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 8th percentile — 8.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.001
Affected products
- Appsup-Dart Jose — versions < 0.3.5+1
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-34240?
- CVE-2026-34240 is a high-severity vulnerability in Appsup-Dart Jose, classified under Improper Verification of Cryptographic Signature. CVSS score: 7.5/10. Published 2026-03-31.
- How severe is CVE-2026-34240?
- High severity. CVSS v3 base score is 7.5 out of 10.