CVE-2026-82730

ash_typescript (from 0.11.0 before 0.18.0) mishandles Ash.ForbiddenField markers when serializing RPC results, so attribute values that Ash field policies denied are returned to the caller with their real contents hidden inside the marker that represents the denial. The flaw is triggered when an Ash action returns an embedded resource as a map, which routes through normalize_resource_struct/2 with an empty template, or through the public, unguarded normalize_value_for_json/1 entry point; in both cases normalize_primitive/1 lacks a clause to strip the marker and a generic struct branch serializes every key, including original_value. Because the CVSS 4.0 score is 8.2 with no privileges required, an unauthenticated RPC caller gains read access to policy-denied attribute values, a confidentiality-only issue with no integrity or availability impact. Only applications built on the Elixir Ash framework that use the ash_typescript RPC layer and enforce field policies, particularly over embedded resources, are affected. No public proof-of-concept, KEV listing, or known in-the-wild exploitation exists, and EPSS is 0.3%.

What to do: Upgrade to ash_typescript 0.18.0 or later, which adds the missing marker-stripping clause in result normalization. In the interim, audit RPC actions that return embedded resources as maps and any direct calls to AshTypescript.Rpc.ResultProcessor.normalize_value_for_json/1, and verify that field-policy-denied attributes are not being echoed back to RPC callers in responses.