CVE-2026-53716: Envoy Gateway: Wasm HTTP fetch decompresses gzip without output-size limit

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

Preconditions (4):

• Tenant can create EnvoyExtensionPolicy (baseline)
• Attacker hosts a gzip-bomb at a reachable URL
• sha256 unset (optional field; check is post-decompression anyway)
• No operator Wasm-URL allowlist (none exists in code)

Description

getFileFromGZ calls io.ReadAll on a raw gzip.Reader (httpfetcher.go:216) with no output bound, while the compressed input is capped at 256 MiB (httpfetcher.go:139). The bytes originate from a tenant-controlled EnvoyExtensionPolicy.spec.wasm[].code.http.url (envoyextensionpolicy.go:1077 → cache.go:248 → httpfetcher.go:147 → :233), so an untrusted tenant can point at a ~10 MiB gzip-of-zeros and force ~10 GiB allocation in the shared controller process. All candidate guards execute either before the body is buffered or after decompression. OOM-kills, restarts, re-reconciles same CR, crash-loops — persistent cross-tenant control-plane outage with PR:L/AC:L and scope change → HIGH despite availability-only.