EEF-CVE-2026-54894

## Summary

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.to\_atom/1. base\_key/1 in lib/guardian/plug/keys.ex converts any binary into the atom :"guardian\_<input>", and the derived helpers claims\_key/1, resource\_key/1, and token\_key/1 create a second atom on top of that. key\_from\_other/1 likewise converts a regex-captured binary through String.to\_atom/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.current\_token(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.

## Workaround

Do not derive Guardian keys from untrusted input. Use a fixed, hardcoded set of namespace keys, or validate the value against a bounded allowlist of known keys, before passing it as the :key option.

## Configuration

Only applications that derive a Guardian key (the conn/session namespace) from attacker-influenced data are exploitable. This is the case when a caller-supplied value such as a tenant identifier, request header, or other request input is passed as the :key option to entry points like Guardian.Plug.current\_token/2. Applications that use a static namespace (the default :default key or hardcoded atoms) are not affected.