CVE-2026-54894

Allocation of Resources Without Limits or Throttling in ueberauth guardian allows denial of service via unbounded atom creation from attacker-influenced binary input.

Guardian.Plug.Keys derives connection and session namespace keys by passing arbitrary binaries to String.toatom/1. basekey/1 in lib/guardian/plug/keys.ex converts any binary into the atom :"guardian<input>", and the derived helpers claimskey/1, resourcekey/1, and tokenkey/1 create a second atom on top of that. keyfromother/1 likewise converts a regex-captured binary through String.toatom/1. The public specs advertise String.t() as a valid argument, so passing a string is documented usage, and higher-level entry points such as Guardian.Plug.currenttoken(conn, key: key) thread the caller-supplied key straight into these functions.

String.to_atom/1 creates a brand-new atom for every previously unseen binary, atoms are never garbage collected, and the BEAM atom table is fixed at roughly 1,048,576 entries by default. An application that routes attacker-influenced data (a tenant identifier, header, or other request input) into a Guardian key therefore mints one permanent atom per distinct value. A modest stream of varied, unauthenticated input permanently consumes the atom table and crashes the BEAM node, taking down every application running on it.

This issue affects guardian: from 0.1.0 before 2.4.1.