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CVE-2026-94201 – Denial of Service (Atom Table Exhaustion) – Ash Framework 3.5.1 through 3.34.2

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Summary

CVE-2026-94201 is a denial-of-service vulnerability in the Ash Framework, a data layer and application framework for Elixir, caused by uncontrolled atom creation when filtering on :atom-typed resource attributes. An unauthenticated or low-privileged remote actor who can supply filter values to a public, filterable atom attribute can force the application to permanently exhaust the BEAM virtual machine’s finite atom table, crashing the node. The issue carries a CVSS score of 8.2 (High) and affects Ash versions 3.5.1 through 3.34.2.

Technical details

  • Root cause: Ash.Type.Atom did not implement a coerce/2 callback. When an attacker-controlled value was filtered against an atom attribute configured with unsafe_to_atom?: true, Ash’s filter-coercion path fell back to cast_input/2, which calls Elixir’s String.to_atom/1.
  • Why it’s dangerous: In the BEAM (Erlang VM) runtime, atoms are never garbage collected and the atom table has a fixed maximum size. Calling String.to_atom/1 on attacker-supplied, non-repeating strings permanently interns a new atom for every distinct filter value submitted.
  • Trigger conditions: A resource must expose a public, filterable :atom attribute with the unsafe_to_atom?: true constraint, reachable through a query interface such as AshGraphql, AshJsonApi, or Ash.Query.filter_input/2.
  • Notably exposed component: AshPaperTrail version resources are especially at risk, since their default version_action_name attribute is an atom attribute configured with unsafe_to_atom?: true out of the box.
  • Attack vector: Network — no authentication beyond the ability to submit filter parameters is required, and no user interaction is needed.
  • Impact: Repeated submission of unique filter values exhausts the BEAM atom table, ultimately crashing the Erlang VM and taking down the entire application node (availability impact only; no confidentiality or integrity impact).

Affected software

  • Package: ash (Hex/Elixir), vendor ash-project
  • Vulnerable versions: 3.5.1 through 3.34.2
  • Fixed version: 3.34.3 and later
  • Affected module: Ash.Type.Atom (lib/ash/type/atom.ex)
  • Applications using Ash resources with public, filterable :atom attributes configured with unsafe_to_atom?: true (including deployments using AshPaperTrail’s default version resource configuration) are at heightened risk.

Severity

  • CVSS Score: 8.2 (High)
  • CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
  • CWE-770: Allocation of Resources Without Limits or Throttling

Mitigation and recommended actions

  • Immediate: Upgrade ash to version 3.34.3 or later, which adds a coerce/2 callback to Ash.Type.Atom that avoids interning new atoms during filtering while preserving existing unsafe_to_atom? behavior for direct attribute assignment.
  • If immediate patching is not possible:
    • Audit resources for public, filterable :atom attributes with unsafe_to_atom?: true, and restrict or remove filter access on these attributes until patched.
    • Pay particular attention to AshPaperTrail-generated version resources, which expose this configuration by default.
    • Monitor BEAM atom table usage/consumption metrics and application availability for signs of exploitation attempts.

References

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