sigstore-js failed to properly verify the authenticity of bundled data, deriving a transparency‑log timestamp from an integratedTime field that is not cryptographically bound to the inclusion proof. An attacker who can supply an untrusted bundle could manipulate certificate validity and the timestamp threshold used by the library, potentially allowing forged or modified signed content to be accepted. This flaw falls under CWE‑345, which involves insecure handling of cryptographic data verification.

sigstore-js customers using the @sigstore/verify JavaScript library before version 3.1.1 are vulnerable. Versions 3.0.x and 3.1.0 lack the fix that binds the timestamp to the inclusion proof.

The CVSS score of 6.5 classifies this as a moderate severity issue, and the EPSS score indicates a very low likelihood of exploitation. Based on the description, it is inferred that the most likely attack vector involves local or remote injection of malicious bundles through an application that relies on sigstore‑js, rather than a background exploitation of vulnerable clients.