Kyverno APICall SSRF Vulnerability Leading to Multi-Tenant Isolation Breach
Date: 2026-04
Affected: go/github.com/kyverno/kyverno
Attack vector: ssrf
Category: vulnerability-disclosure
Severity: High
CWE: CWE-918
CVSS: 7.7 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N)

### Summary Kyverno's APICall feature contains a Server-Side Request Forgery (SSRF) vulnerability that allows users with Policy creation permissions to access arbitrary internal resources through Kyverno's high-privilege ServiceAccount. In multi-tenant Kubernetes environments, this constitutes a classic Confused Deputy problem: low-privilege tenants can steal sensitive data from other tenants (such as database passwords and API keys) and cloud platform IAM credentials, completely breaking tenant isolation. This vulnerability does not require cluster-admin privileges and can be exploited with only namespace-level Policy creation permissions. ### Details #### Vulnerability Mechanism Kyverno's APICall feature allows Policies to fetch external data via HTTP requests. This feature does not validate target URLs when executing HTTP requests, leading to an SSRF vulnerability. **Source Point - User-Controlled URL** File: `api/kyverno/v1/common_types.go`, lines 247-250 ```go type ServiceCall struct { // URL is the JSON web service URL URL string `json:"url"` // User-controlled, no validation Headers []HTTPHeader `json:"headers,omitempty"` CABundle string `json:"caBundle,omitempty"` } ``` The URL field is completely controlled by users through Policy configuration, with no validation mechanism to restrict target addresses. **Sink Point - HTTP Request Execution** File: `pkg/engine/apicall/executor.go`, lines 65-110 ```go func (a *executor) executeServiceCall(c


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Architectural layers (MAESTRO):