CVE-2026-94201: CWE-770 Allocation of Resources Without Limits or Throttling in ash-project ash

The vulnerability arises because ash stores :atom-typed attributes as strings and compares them as strings. When filtering on such an attribute configured with unsafe_to_atom?: true, the comparison value is coerced via Ash.Type.Atom. Since Ash.Type.Atom lacked a coerce/2 callback, coercion defaulted to cast_input/2, which calls String.to_atom/1, interning a new atom for every distinct filter value. Atoms in the BEAM VM are never garbage collected and the atom table has a fixed size. An attacker supplying many distinct filter strings can exhaust the atom table, causing a denial of service by crashing the node. The fix introduces a coerce/2 function that prevents interning atoms during filtering comparisons, leaving comparison values as strings. This fix does not change setting attributes from action input, which still uses cast_input/2 and honors unsafe_to_atom?.

An unauthenticated attacker able to supply filter values for a public, filterable :atom attribute with unsafe_to_atom?: true can exhaust the BEAM atom table by causing many distinct atoms to be interned. This leads to a denial of service via node crash. The vulnerability affects publicly filterable atom attributes such as those in AshPaperTrail's version resources. There is no indication of remote code execution or data leakage, but the denial of service impact is high.

A fix is available that adds a coerce/2 callback to Ash.Type.Atom to avoid interning atoms during filtering comparisons. Users should upgrade to ash version 3.34.3 or later where this fix is included. Until then, avoid exposing public, filterable :atom attributes with unsafe_to_atom?: true or restrict access to mitigate exploitation risk.