---
id: CVE-2026-55733
title: >-
  Allocation of Resources Without Limits or Throttling in ueberauth guardian
  allows denial of service via unbounded atom creation from attacker-controlled
  binary input.


  Guardian.Permissions.AtomEncoding encodes permission scopes by passin…
summary: >-
  Allocation of Resources Without Limits or Throttling in ueberauth guardian
  allows denial of service via unbounded atom creation from attacker-controlled
  binary input.


  Guardian.Permissions.AtomEncoding encodes permission scopes by passin…
severity: none
cwe:
  - CWE-770
published: '2026-08-01'
updated: '2026-08-01'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55733'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-55733.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ueberauth/guardian/commit/9cd268557846aa4c3ad53566c08f2c190ee5513f
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ueberauth/guardian/security/advisories/GHSA-fjr5-7xrc-hmpj
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-55733'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
ingestedAt: '2026-08-02T09:18:11.879Z'
epss: 0.00322
epssPercentile: 0.2552
---

## Overview

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

Guardian.Permissions.AtomEncoding encodes permission scopes by passing arbitrary binaries to String.to_atom/1. When encode/3 in lib/guardian/permissions/atom_encoding.ex is called with a list, each binary entry is handled by the encode_value/3 binary clause, which calls String.to_atom(value) with no allow-list check. The perm_set argument (the application's small, finite set of legitimate permission names) is discarded, so any external string flows straight into atom creation. This encoder is selected with use Guardian.Permissions, encoding: Guardian.Permissions.AtomEncoding and reached through the imported encode/3 entry point.

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 funnels attacker-influenced permission scopes (from a request body, a JWT claim, or other external input) into encode/3 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 with system_limit, taking down every application running on it.

The default encoder is Guardian.Permissions.BitwiseEncoding, which is not affected.

This issue affects guardian: from 2.0.0 before 2.4.1.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.