The vulnerability lies in the preAuthEncoding function of @sigstore/core prior to version 3.2.1, where Node.js ascii encoding converts the Pre‑Authentication Encoding string to bytes in a way that allows the payloadType field to be altered after the signature has been created. This type‑binding failure (CWE‑347) breaks DSSE’s guarantee that the payload type remains unchanged, enabling an attacker to present a modified artifact as authentic without invalidating the signature.

The affected product is sigstore-js, a JavaScript library suite for interacting with Sigstore services. All releases that incorporate @sigstore/core before version 3.2.1 are vulnerable.

The CVSS score of 5.4 indicates moderate severity, and the EPSS score of under 1 % implies a low likelihood of exploitation currently. The vulnerability is not listed in the CISA KEV catalog. Exploitation requires the vulnerable library to be used in an environment where a payloadType can be altered after signature generation, so the risk is limited to dependency‑based scenarios rather than a broad network attack surface.