Fulcio has OIDC Discovery Redirect Following Allows SSRF and JWKS Substitution for Meta-Issuer Paths, with Kubernetes Service-Account Token Leakage

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No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Fulcio is a certificate authority for issuing code signing certificates for an OpenID Connect (OIDC) identity. Versions through 1.8.5 improperly follow cross-host redirects and attach Kubernetes ServiceAccount tokens during OIDC discovery, allowing a malicious or compromised issuer to perform blind SSRF, substitute and cache malicious JWKS keys, or disclose ServiceAccount tokens to external hosts. Version 1.8.6 blocks cross-host redirects, restricts token injection, and restricts local token loading. No known workarounds are available.

Source published

13 Aug 2026 13:08:21 UTC

Source modified

15 Aug 2026 03:14:47 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 8.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Fulcio is a certificate authority for issuing code signing certificates for an OpenID Connect (OIDC) identity. Versions through 1.8.5 improperly follow cross-host redirects and attach Kubernetes ServiceAccount tokens during OIDC discovery, allowing a malicious or compromised issuer to perform blind SSRF, substitute and cache malicious JWKS keys, or disclose ServiceAccount tokens to external hosts. Version 1.8.6 blocks cross-host redirects, restricts token injection, and restricts local token loading. No known workarounds are available.

Source published

Aug 13, 2026, 1:08:21 PM (timezone not stated)

Source modified

Aug 15, 2026, 3:14:47 AM (timezone not stated)

Observed here

7 Nov 2026 11:31:58 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 8.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Fulcio is a certificate authority for issuing code signing certificates for an OpenID Connect (OIDC) identity. Versions through 1.8.5 improperly follow cross-host redirects and attach Kubernetes ServiceAccount tokens during OIDC discovery, allowing a malicious or compromised issuer to perform blind SSRF, substitute and cache malicious JWKS keys, or disclose ServiceAccount tokens to external hosts. Version 1.8.6 blocks cross-host redirects, restricts token injection, and restricts local token loading. No known workarounds are available.

Source published

13 Aug 2026 13:19:09 UTC

Source modified

24 Oct 2026 16:10:00 UTC

Observed here

25 Oct 2026 12:17:38 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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CVSS 3.1 · [email protected] · Secondary · 8.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

## Impact Three security vulnerabilities were identified in the OIDC Discovery client: 1. **Blind Server-Side Request Forgery (SSRF) via Cross-Host Redirects**: Fulcio uses an HTTP client to fetch OIDC discovery metadata (`/.well-known/openid-configuration`). Prior to this fix, if a configured issuer returned an HTTP redirect to a different host, the client followed it by default. This allowed a compromised or malicious issuer to redirect Fulcio's discovery requests to internal-only systems, resulting in blind SSRF. 2. **JWKS Substitution and Cache Poisoning**: Because cross-host redirects were permitted during OIDC discovery, an attacker could manipulate the discovery flow to return a malicious `jwks_uri` pointing to an attacker-controlled host. When Fulcio successfully initialized the provider and cached the resulting verifier in the verifier cache, it poisoned the cache with the attacker's verification keys. The attacker could then present signatures validated against the poisoned keys. 3. **Kubernetes ServiceAccount Token Leakage**: Fulcio mounts an in-cluster Kubernetes ServiceAccount token to authenticate OIDC discovery requests sent to the local control plane API server (`https://kubernetes.default.svc`). * **Cross-Host Redirects & JWKS**: The token was previously attached globally by the transport, leaking it to third-party hosts if the issuer performed a redirect or if the `jwks_uri` pointed to a different domain. * **Wildcard MetaIssuers**: If a wildcard `MetaIssuer` of type `kubernetes` (e.g., matching external EKS/GKE endpoints) was matched, and a local Kubernetes issuer was present in the config, the transport loaded and attached the local in-cluster ServiceAccount token to outbound requests sent to the external host. ## Patches The following mitigations have been applied: * **Blocked Cross-Host Redirects**: A custom callback is configured on all OIDC discovery HTTP clients to reject redirects that attempt to cross the original issuer's host boundary. * **Restricted Token Injection**: Updated the transport to only attach the ServiceAccount token when the outgoing request's host exactly matches the configured host of the issuer. * **Restricted Local Token Loading**: Constrained the loader to only load and wrap the transport with the local ServiceAccount token when the target issuer URL exactly matches the private local API server (`https://kubernetes.default.svc`). ## Workarounds None, upgrade to v1.8.6

Source published

30 Jun 2026 18:38:45 UTC

Source modified

10 Sep 2026 03:50:49 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Publisher rating · HIGH

Fulcio has OIDC Discovery Redirect Following Allows SSRF and JWKS Substitution for Meta-Issuer Paths, with Kubernetes Service-Account Token Leakage in github.com/sigstore/fulcio

Source published

7 Jul 2026 15:26:32 UTC

Source modified

10 Jul 2026 18:29:34 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.