CVE-2026-49478
Description
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.
Statement
A flaw was found in Fulcio's OIDC Discovery client. Three related vulnerabilities allow exploitation when a configured OIDC issuer is compromised or malicious: (1) Blind SSRF — the discovery client follows cross-host HTTP redirects, allowing a malicious issuer to redirect Fulcio's metadata fetch requests to internal-only systems (e.g., cloud IMDS endpoints, RFC 1918 addresses); (2) JWKS substitution — the redirected discovery flow can return a manipulated jwks_uri pointing to an attacker-controlled host, poisoning the verifier cache with attacker keys and enabling validation of attacker-controlled signatures; (3) Kubernetes ServiceAccount token leakage — the in-cluster SA token is attached globally by the HTTP transport, leaking it to third-party hosts during cross-host redirects or when wildcard MetaIssuers match external endpoints. Exploitation requires a compromised or malicious OIDC issuer already trusted in the Fulcio configuration. In typical Red Hat Trusted Artifact Signer deployments, OIDC issuers are explicitly configured and curated, reducing the attack surface."}]
Mitigation
Upgrade to Fulcio v1.8.6 or later. No workaround is available.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.5 | N/A | 8.7 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Changed |
| Confidentiality | High | N/A | High |
| Integrity Impact | Low | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
Red Hat CVSS v3 Score Explanation
S:C→U (impact within Fulcio trust boundary), I:H→L (JWKS cache poisoning requires specific timing and attacker must maintain malicious issuer configuration). K8s SA token leak is bounded to Fulcio pod SA permissions.
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Application Data
Integrity
Technical Impact: Execute Unauthorized Code or Commands
Access Control
Technical Impact: Bypass Protection Mechanism
By providing URLs to unexpected hosts or ports, attackers can make it appear that the server is sending the request, possibly bypassing access controls such as firewalls that prevent the attackers from accessing the URLs directly. The server can be used as a proxy to conduct port scanning of hosts in internal networks, use other URLs such as that can access documents on the system (using file://), or use other protocols such as gopher:// or tftp://, which may provide greater control over the contents of requests.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
