CVE-2026-55636

Vulnerability in Capsule, a multi-tenancy and policy-based framework for Kubernetes. The Capsule Controller runs with cluster-admin privileges. TenantResource RawItems processing incorrectly handles cluster-scoped resources, allowing tenant administrators to create cluster-scoped resources (e.g., ClusterRole, ValidatingWebhookConfiguration) with elevated privileges, leading to cross-tenant privilege escalation and cluster-level attacks. Version 0.13.0 patches this issue.

Capsule from version 0.13.0 to 0.13.7 has a vulnerability in the Tenant validation webhook where the new and old parameters are reversed, causing validation of the previous AllowedHostnames.Regex instead of the submitted value. A cluster administrator can store a malformed regex, which later blocks Ingress operations for the tenant. Fixed in version 0.13.7.

Capsule from version 0.13.0 to 0.13.7 has a vulnerability in Tenant update validation where ForbiddenLabels.Regex is compiled for both labels and annotations checks instead of validating ForbiddenAnnotations.Regex. An administrator can persist a malformed regex, which later causes regexp.MustCompile to panic during metadata validation and blocks namespace operations. Fixed in version 0.13.7.

In Capsule prior to 0.13.7, ForbiddenListSpec.ExactMatch in pkg/api/forbidden_list.go sorts denied metadata keys case-insensitively and then uses sort.SearchStrings, which assumes byte-order sorting. When the forbidden list mixes capitalized and lowercase keys, the binary search can return false for a key that is present. An authenticated tenant owner can bypass configured namespace, Service, or delegated node metadata restrictions. This is fixed in version 0.13.7.

Capsule from 0.13.0 to 0.13.8 (after incomplete CVE-2026-22872 fix) did not apply cluster-scoped resource rejection guards, allowing a Tenant Owner to create cluster-scoped resources like ClusterRole or ValidatingWebhookConfiguration via the cluster-admin controller client.

Capsule before 0.13.8 did not validate regular expressions in CapsuleConfiguration for ForbiddenLabels and ForbiddenAnnotations. A Cluster Admin could store malformed regex that crashed the node admission webhook on node create, update, or patch requests.

In Capsule for Kubernetes prior to 0.13.0, a vulnerability allowed namespace hijacking via namespace/finalize and namespace/status subresources. The validating webhook does not intercept these subresources, allowing a tenant admin to modify namespace metadata.