Filter expression injection via forged keyset pagination cursor in Ash

Deserialization of Untrusted Data vulnerability in ash-project ash allows an unauthenticated attacker to inject a filter expression through a forged keyset pagination cursor, resulting in SQL injection or code execution depending on the data layer. Read actions with keyset pagination decode the client-supplied page[:after] or page[:before] cursor in decode_values/2 in lib/ash/page/keyset.ex using non_executable_binary_to_term/2 with [:safe]. That guard blocks new atoms, funs, and ports, but not a struct built from atoms already interned in a running Ash application, so a decoded %Ash.Query.Call{} expression survives and is spliced into the keyset filter as a comparison value in do_filters/4 and evaluated. Because the cursor bypasses the Ash.Expr macro, the runtime never applies the private?/public? gate that would otherwise reject it. On AshPostgres the injected fragment is inlined into the SQL query; on the ETS and Simple data layers it is evaluated in-process as an arbitrary function call. This issue affects ash: from 1.17.0 before 3.31.3.

Attacker-influenced serialised data is reconstructed as trusted objects, which can invoke dangerous application behaviour.

An attacker operating through local access may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.