Attack Chain

1. Attacker crafts malicious artifact: An attacker creates a malicious software package or artifact intended for distribution.
2. Attacker obtains unauthorized signing certificate: The attacker acquires a certificate that meets general validity criteria (e.g., correct issuer, valid dates) but lacks specific critical OID extensions that the target application's sigstore configuration intends to enforce via certificateOIDs.
3. Attacker signs malicious artifact: The attacker signs the malicious artifact using their unauthorized certificate.
4. Target system attempts to verify artifact: A target system, using a vulnerable npm/sigstore library (<= 4.1.0) and configured with certificateOIDs to enforce specific OID policies, attempts to verify the signed artifact.
5. sigstore silently drops OID constraints: Due to the vulnerability, the npm/sigstore library's createVerificationPolicy() function silently ignores the certificateOIDs parameter when constructing the verification policy.
6. Artifact falsely deemed legitimate: The signed malicious artifact passes sigstore verification because the critical OID extension check, which should have rejected the unauthorized certificate, was never applied.
7. Malicious artifact executed/deployed: The target system proceeds to trust and potentially execute or deploy the malicious artifact, believing it to be legitimately signed and compliant with its security policies.

Impact

Applications integrating the npm/sigstore library that depend on the certificateOIDs feature for robust certificate policy enforcement are rendered vulnerable to supply chain attacks. This vulnerability means that unauthorized or non-compliant certificates, which should be explicitly rejected based on missing or incorrect OID extensions, will instead be accepted by the verification process. The direct consequence is that organizations relying on this library for software supply chain integrity could inadvertently trust and deploy malicious artifacts. This could lead to a wide range of impacts, including system compromise, data exfiltration, or the introduction of backdoors, undermining the entire purpose of artifact signing and verification. The exact number of affected organizations is difficult to ascertain, but any user of npm/sigstore up to version 4.1.0 configured with certificateOIDs is at risk.

Recommendation

• Patch CVE-2026-48815 immediately: Upgrade npm/sigstore to a patched version (4.1.1 or later) to address CVE-2026-48815, ensuring certificateOIDs are correctly enforced during verification.
• Review sigstore configurations: Audit all sigstore.verify() and createVerifier() calls in your codebase to confirm that certificate validation logic correctly identifies and rejects certificates that do not meet expected OID constraints, even after patching.