【高危】fulcio：服务端请求伪造风险（GHSA-f5mr-q85p-6hh6）

安全情报快照 · 风险级别：高危 · CVSS：8.7 · CVE-2026-49478 · GHSA-f5mr-q85p-6hh6

先看结论

fulcio存在服务端请求伪造风险，<= 1.8.5 受影响，建议升级至 1.8.6。

影响范围

处置建议

优先将 github.com/sigstore/fulcio 升级至 1.8.6 或更高版本；升级前请结合业务依赖完成兼容性验证。

上游技术详情（原文）

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

来源与许可

• GitHub Advisory GHSA-f5mr-q85p-6hh6
• https://github.com/sigstore/fulcio/security/advisories/GHSA-f5mr-q85p-6hh6

本页自动同步 GitHub Advisory Database 的公开数据，并保留上游原文供核验；不宣称原创分析。数据许可：CC-BY-4.0。