CVE-2026-53717: Envoy Gateway: OCI layer extraction allocates make([]byte, h.Size) from untrusted tar header

Vulnerability report without repro case. Repro case may be added later after harness is complete.

Preconditions (4):

• Tenant can create EnvoyExtensionPolicy (baseline)
• Controller has egress to attacker-controlled OCI registry
• No registry allowlist (none exists in code)
• Layer presents Docker/OCI media type

Description

At imagefetcher.go:287, make([]byte, h.Size) uses the attacker-controlled tar-header size; the LimitReader at :278 bounds bytes read from the stream but not the header-declared size returned by tr.Next() (a 512-byte header can claim a multi-TB entry via PAX/GNU encoding). Reached from untrusted tenant input via EnvoyExtensionPolicy spec.wasm[].code.image.url (envoyextensionpolicy.go:1157 → cache.go:262/299 → imagefetcher.go:218 → :287), and the allocation happens for every tar entry regardless of filename. The resulting Go runtime OOM throw is unrecoverable and, because the CRD persists, crash-loops the shared controller — single-request, non-volumetric, cluster-wide DoS.