Ash stores :atom-typed attributes as strings and compares them as strings. When such an attribute is referenced in a filter, the comparison value is coerced through Ash.Type.Atom. Because the type defined no coerce/2 callback, coercion fell back to the default (cast_input/2), which calls String.to_atom/1 when the attribute is configured with the unsafe_to_atom?: true constraint.

Filtering such an attribute with attacker-controlled strings therefore interned a new, permanent atom for every distinct value. Atoms are never garbage collected and the BEAM caps the atom table, so an actor who can supply filter values for a public, filterable :atom attribute declared with unsafe_to_atom?: true can exhaust the atom table and crash the node (denial of service). AshPaperTrail is a notable example: its version resources expose a public, filterable version_action_name atom attribute with unsafe_to_atom?: true by default.

The fix adds a coerce/2 to Ash.Type.Atom that never interns atoms — a comparison value is left as a string, since the type is stored and compared as a string. Setting the attribute from action input (cast_input/2, which still honors unsafe_to_atom?) is unchanged.

This issue affects ash: from 3.5.1 before 3.34.3.
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History

Mon, 05 Oct 2026 19:30:00 +0000

Type Values Removed Values Added
Description Ash stores :atom-typed attributes as strings and compares them as strings. When such an attribute is referenced in a filter, the comparison value is coerced through Ash.Type.Atom. Because the type defined no coerce/2 callback, coercion fell back to the default (cast_input/2), which calls String.to_atom/1 when the attribute is configured with the unsafe_to_atom?: true constraint. Filtering such an attribute with attacker-controlled strings therefore interned a new, permanent atom for every distinct value. Atoms are never garbage collected and the BEAM caps the atom table, so an actor who can supply filter values for a public, filterable :atom attribute declared with unsafe_to_atom?: true can exhaust the atom table and crash the node (denial of service). AshPaperTrail is a notable example: its version resources expose a public, filterable version_action_name atom attribute with unsafe_to_atom?: true by default. The fix adds a coerce/2 to Ash.Type.Atom that never interns atoms — a comparison value is left as a string, since the type is stored and compared as a string. Setting the attribute from action input (cast_input/2, which still honors unsafe_to_atom?) is unchanged. This issue affects ash: from 3.5.1 before 3.34.3.
Title Filtering an :atom attribute with unsafe_to_atom? can exhaust the BEAM atom table in Ash
First Time appeared Ash-project
Ash-project ash
Weaknesses CWE-770
CPEs cpe:2.3:a:ash-project:ash:*:*:*:*:*:*:*:*
Vendors & Products Ash-project
Ash-project ash
References
Metrics cvssV4_0

{'score': 8.2, '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'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: EEF

Published:

Updated: 2026-10-05T19:19:51.326Z

Reserved: 2026-09-24T09:15:02.216Z

Link: CVE-2026-94201

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-05T20:17:28.693

Modified: 2026-10-05T20:17:28.693

Link: CVE-2026-94201

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-05T21:15:15Z

Weaknesses