sigstore-java CVE-2026-48791

Exploitation requires the attacker to have already obtained local system access AND to have successfully exfiltrated the ephemeral private key used during a prior Sigstore signing operation - the vendor description explicitly names this as the required precondition. The verifying party must be running exactly dev.sigstore:sigstore-java version 2.0.0; older versions and 2.1.0 are not vulnerable. User interaction is required: the victim or an automated pipeline must invoke bundle verification against the forged artifact. No network-based or unauthenticated exploitation path exists. Limiting factors include: the need for prior system compromise, possession of the specific ephemeral key, and the narrow version window (2.0.0 only).

The CVSS 3.1 vector (AV:L/AC:L/PR:H/UI:R/S:U/C:N/I:L/A:N) yielding a score of 2.0 accurately reflects a very constrained attack surface: local-only access, high privilege (sufficient to exfiltrate a temporary signing key from a user's session), and required victim interaction (triggering bundle verification). There is no confirmed active exploitation and this CVE is not listed in the CISA KEV catalog. A proof-of-concept test bundle exists per the vendor advisory, but it demonstrates the bypass rather than enabling remote or unauthenticated exploitation. EPSS data is not provided in the source intelligence; given the narrow prerequisites, exploitation probability is expected to be extremely low. The integrity impact is limited and unscoped - only artifact signature verification is subverted, with no confidentiality or availability consequence. This vulnerability is low priority for the vast majority of organizations but warrants immediate attention in high-assurance software supply chain pipelines where the integrity of Sigstore-verified artifacts is a security control boundary.

An attacker who has already compromised a developer workstation and exfiltrated the ephemeral private key generated during a prior Sigstore signing session crafts a forged bundle pairing that key with the original, now-expired Fulcio certificate. When a pipeline or developer invokes sigstore-cli verify (or the sigstore-java library directly) on the forged bundle using version 2.0.0, the missing integratedTime check causes verification to succeed silently - a result the vendor-provided PoC bundle demonstrates explicitly against the CLI tool.