Medium [CVE-2026-49478] Server-Side Request Forgery and Kubernetes ServiceAccount token leakage

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.

A flaw was found in Fulcio's OpenID Connect (OIDC) Discovery client. This vulnerability allows a remote attacker to perform Server-Side Request Forgery (SSRF) by redirecting discovery requests to internal systems.

Additionally, an attacker can manipulate the JSON Web Key Set (JWKS) Uniform Resource Identifier (URI) to poison the verifier cache with malicious keys, enabling the validation of attacker-controlled signatures.

Furthermore, the flaw can lead to the leakage of Kubernetes ServiceAccount tokens to third-party hosts through cross-host redirects or misconfigured MetaIssuers, potentially exposing sensitive cluster credentials. Exploitation requires a compromised or malicious OIDC issuer already trusted in the Fulcio configuration.