AIKIDO-2026-634688

TL;DR

The optional Guardian.Permissions.AtomEncoding encoder in lib/guardian/permissions/atom_encoding.ex converts permission scopes into atoms by calling String.to_atom on arbitrary binaries and ignores the application's permission allow-list. An application that opts into this encoder and feeds it externally influenced permission scopes interns one permanent atom per distinct value. Because BEAM atoms are never garbage collected and the atom table is fixed in size, a stream of varied unauthenticated input exhausts the table and crashes the node. The fix validates each value against the permission set and uses String.to_existing_atom instead of minting fresh atoms.