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.
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.
Advisories
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Fixes
Solution
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Workaround
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References
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 |
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| Weaknesses | CWE-770 | |
| CPEs | cpe:2.3:a:ash-project:ash:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Ash-project
Ash-project ash |
|
| References |
| |
| Metrics |
cvssV4_0
|
Projects
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Status: PUBLISHED
Assigner: EEF
Published:
Updated: 2026-10-05T19:19:51.326Z
Reserved: 2026-09-24T09:15:02.216Z
Link: CVE-2026-94201
No data.
Status : Received
Published: 2026-10-05T20:17:28.693
Modified: 2026-10-05T20:17:28.693
Link: CVE-2026-94201
No data.
OpenCVE Enrichment
Updated: 2026-10-05T21:15:15Z
Weaknesses