sigstore-python is a Python tool for generating and verifying Sigstore signatures. Versions of sigstore-python newer than 2.0.0 but prior to 3.6.0 perform insufficient validation of the "integration time" present in "v2" and "v3" bundles during the verification flow: the "integration time" is verified *if* a source of signed time (such as an inclusion promise) is present, but is otherwise trusted if no source of signed time is present. This does not affect "v1" bundles, as the "v1" bundle format always requires an inclusion promise. Sigstore uses signed time to support verification of signatures made against short-lived signing keys. The impact and severity of this weakness is *low*, as Sigstore contains multiple other enforcing components that prevent an attacker who modifies the integration timestamp within a bundle from impersonating a valid signature. In particular, an attacker who modifies the integration timestamp can induce a Denial of Service, but in no different manner than …