EEF-CVE-2026-67579

## Summary

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.

## Configurations

A read action must declare `keyset? true` in its `pagination` block, and the application must pass a client-supplied value as the `:after` or `:before` page option. The severity of a successful attack depends on the data layer: AshPostgres yields SQL injection, while the ETS and Simple data layers evaluate the injected expression in-process.