Is CVE-2026-34240 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-34240 being exploited in the wild.

How severe is CVE-2026-34240?

High severity, with a CVSS score of 7.5, published 31 March 2026.

Is there a fix for CVE-2026-34240?

A patch was published on 2026-03-31. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-34240 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-34240?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-34240: appsup-dart jose token forgery via untrusted JWK header

CVE-2026-34240 · Severity: high · CVSS 7.5 · Published 2026-03-31

A vulnerability in the 'jose' library, which is used to handle secure digital signatures and tokens, allows attackers to bypass security checks. By including their own encryption key within a token's header, an attacker can trick the system into accepting a forged token as legitimate. This could allow unauthorized users to impersonate others or gain access to protected data and services without valid credentials.

Quick answers

Is CVE-2026-34240 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-34240 being exploited in the wild.
How severe is CVE-2026-34240?: High severity, with a CVSS score of 7.5, published 31 March 2026.
Which products and versions are affected?: appsup-dart jose <= 0.3.5.
Is there a fix for CVE-2026-34240?: A patch was published on 2026-03-31. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-34240 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-34240?: Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A vulnerability exists in the 'jose' library (versions <= 0.3.5) due to improper verification of cryptographic signatures (CWE-347). The library's key selection logic in 'JsonWebKeyStore' treats a JSON Web Key (JWK) embedded in the JWS/JWT header as a valid verification candidate, even if that key is not in the application's trusted key store. An unauthenticated remote attacker can exploit this by generating a malicious token, embedding their own public key in the 'jwk' header field, and signing the token with their corresponding private key. The library will then use the attacker's provided key to "successfully" verify the signature, leading to a complete bypass of integrity protections. This issue is patched in version 0.3.5+1.

Affected products

appsup-dart jose <= 0.3.5

Timeline

2026-03-31: disclosed
2026-03-31: advisory
2026-03-31: patched

References

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