https://feed.craftedsignal.io/vendors/sigstore/Trending threats, MITRE ATT&CK coverage, and detection metadata. Fed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioFri, 03 Jul 2026 13:03:14 +0000https://feed.craftedsignal.io/briefs/2026-07-sigstore-fulcio-oidc-ssrf-jwks-cve-2026-49478/Fri, 03 Jul 2026 13:03:14 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2026-07-sigstore-fulcio-oidc-ssrf-jwks-cve-2026-49478/A high-severity vulnerability (CVE-2026-49478) in Sigstore Fulcio's OIDC discovery client allows blind Server-Side Request Forgery (SSRF) via cross-host redirects, facilitates JWKS substitution for cache poisoning, and causes Kubernetes ServiceAccount token leakage to external attackers, potentially compromising supply chain integrity and cluster resources.Three critical security vulnerabilities (CVE-2026-49478) have been identified in the OIDC Discovery client within Sigstore Fulcio versions up to and including 1.8.5. Fulcio, a certificate authority for Sigstore, is crucial for verifying the authenticity of software artifacts in the supply chain. Prior to this fix, Fulcio's OIDC discovery process could be exploited by a malicious or compromised OIDC issuer. This allowed attackers to redirect Fulcio's internal HTTP requests to internal systems, leading to blind Server-Side Request Forgery (SSRF). Furthermore, attackers could poison Fulcio's verifier cache by substituting legitimate JSON Web Key Sets (JWKS) with attacker-controlled ones, enabling the forging of signatures. Compounding these issues, Fulcio's integration with Kubernetes meant ServiceAccount tokens could be leaked to external hosts during OIDC discovery, granting attackers potential access to Kubernetes cluster resources. These flaws severely undermine the integrity and security guarantees provided by Fulcio.

Attack Chain

1. An attacker either controls a malicious OIDC issuer or compromises a legitimate one configured for Fulcio.
2. Fulcio, during its OIDC discovery process, initiates a request to fetch metadata (/.well-known/openid-configuration) from the attacker-controlled OIDC issuer.
3. The malicious OIDC issuer responds with an HTTP 3xx redirect to an internal IP address or hostname within Fulcio's network, such as the Kubernetes API server (https://kubernetes.default.svc), triggering a blind SSRF.
4. Simultaneously, the attacker-controlled issuer can provide a jwks_uri in its discovery response that points to an endpoint under the attacker's control.
5. Fulcio, following the malicious jwks_uri, fetches the attacker's JSON Web Key Set (JWKS) and caches it, effectively poisoning its internal verifier cache.
6. With the poisoned cache, the attacker can now forge signatures for software artifacts that Fulcio will validate as legitimate, bypassing critical integrity checks in the supply chain.
7. During these redirected HTTP requests and JWKS fetches, Fulcio inappropriately attaches its mounted Kubernetes ServiceAccount token to outbound requests directed towards the external, attacker-controlled hosts.
8. This leakage exposes the Kubernetes ServiceAccount token to the attacker, potentially enabling further reconnaissance, privilege escalation, and direct access to the Kubernetes cluster API and its resources.

Impact

The identified vulnerabilities have severe consequences across several domains. The blind SSRF allows attackers to probe and potentially interact with internal network services and infrastructure that would otherwise be inaccessible, potentially revealing sensitive information or enabling further internal attacks. JWKS substitution directly compromises the integrity verification process, allowing attackers to sign and distribute malicious software that appears legitimate, undermining the trust model of Sigstore and supply chain security. Most critically, the leakage of Kubernetes ServiceAccount tokens provides attackers with credentials that can be used to gain unauthorized access to the Kubernetes cluster. This can lead to full cluster compromise, data exfiltration, resource manipulation, and deployment of malicious workloads, affecting a wide range of organizations using Fulcio for artifact signing and verification, particularly those deployed within Kubernetes environments.

Recommendation

• Upgrade immediately: Patch affected Sigstore Fulcio instances to version 1.8.6 or newer to address CVE-2026-49478.
• Monitor application logs: Review application logs for Fulcio's OIDC discovery process for unusual HTTP redirects or fetches from unexpected jwks_uri endpoints, although the SSRF is blind and direct detection may be challenging.
• Review Kubernetes ServiceAccount usage: Audit the permissions granted to the Kubernetes ServiceAccounts used by Fulcio to ensure they adhere to the principle of least privilege, minimizing the impact of potential token leakage as described in CVE-2026-49478.

]]>highadvisorysupply-chain-securitykubernetesoidcssrfjwkscvehttps://feed.craftedsignal.io/briefs/2026-07-sigstore-oid-bypass/Fri, 03 Jul 2026 12:37:11 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2026-07-sigstore-oid-bypass/A high-severity vulnerability (CVE-2026-48815) in the `npm/sigstore` library (versions <= 4.1.0) causes the `certificateOIDs` verification constraint to be silently ignored, allowing applications to accept unauthorized certificates that should have been rejected based on extension policy, which could lead to supply chain attacks by trusting malicious artifacts.A significant security vulnerability, identified as CVE-2026-48815, affects the npm/sigstore JavaScript library in versions up to and including 4.1.0. This flaw stems from a critical oversight in the library's certificate verification logic: while the public sigstore.verify() API accepts the certificateOIDs option, which is intended to enforce specific object identifiers (OIDs) within a certificate's extensions, this constraint is silently dropped during policy construction. Consequently, applications that rely on certificateOIDs to restrict accepted certificates for artifact signing are left without this crucial protection. An attacker could exploit this by presenting a certificate lacking the expected OIDs, yet still satisfying other verification checks, thereby bypassing a key policy enforcement mechanism and potentially enabling the trust of unauthorized or malicious software artifacts in a supply chain.

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.

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