CVE-2026-65834
Summary
CapsuleConfiguration.Spec.NodeMetadata.ForbiddenLabels.Regex and ForbiddenAnnotations.Regex are never validated by any admission webhook. A Cluster Admin can persist a malformed regex to etcd without being blocked. Once stored, every Node CREATE, UPDATE, or PATCH request triggers regexp.MustCompile() in pkg/api/forbidden_list.go:36, which panics and crashes the node admission webhook — causing a cluster-wide Denial of Service for all Node operations.
Root cause
internal/webhook/tenant/validation/ contains dedicated regex validators for every Tenant regex field (hostname, storageclass, ingressclass, containerregistry, etc.). internal/webhook/cfg/ contains no regex validator at all — only owners.go, serviceaccount.go, and warnings.go.
The downstream consumer internal/webhook/node/user_metadata.go calls:
// line 131
matched = forbiddenLabels.RegexMatch(label)
// line 150
matched = forbiddenAnnotations.RegexMatch(annotation)
Which routes to pkg/api/forbidden_list.go:36:
func (in ForbiddenListSpec) RegexMatch(value string) (ok bool) {
if len(in.Regex) > 0 {
ok = regexp.MustCompile(in.Regex).MatchString(value) // ← panics on invalid regex
}
return ok
}
Unlike regexp.Compile, regexp.MustCompile panics instead of returning an error. Since no webhook validates the CapsuleConfiguration regex fields before storage, a malformed value reaches MustCompile on every Node admission request.
Comparison with existing CVEs
GHSA-f94q-w3w8-cj67 and GHSA-gxjc-74v5-3vx3 affect individual Tenant fields — their validators existed but checked the wrong field. This issue is different: no validator exists at all for CapsuleConfiguration regex fields, and the blast radius is cluster-wide (all Nodes), not scoped to one tenant.
PoC
package main
import (
"fmt"
"regexp"
)
type ForbiddenListSpec struct{ Regex string }
// Exact copy of pkg/api/forbidden_list.go:34-38
func (in ForbiddenListSpec) RegexMatch(value string) bool {
if len(in.Regex) > 0 {
return regexp.MustCompile(in.R
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Exploitation outlook
- Low exploitation risk0.27% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 19% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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