{"affected":[{"package":{"ecosystem":"Hex","name":"guardian","purl":"pkg:hex/guardian"},"ranges":[{"events":[{"introduced":"2.0.0"},{"fixed":"2.4.1"}],"type":"SEMVER"}],"versions":["2.0.0","2.1.1","2.1.2","2.2.0","2.2.1","2.2.2","2.2.3","2.2.4","2.3.0","2.3.1","2.3.2","2.4.0"]},{"ranges":[{"events":[{"introduced":"b7a6128ca4d0ffb7f7df5219dd982304ff9d6802"},{"fixed":"9cd268557846aa4c3ad53566c08f2c190ee5513f"}],"repo":"https://github.com/ueberauth/guardian","type":"GIT"}]}],"aliases":["GHSA-fjr5-7xrc-hmpj","CVE-2026-55733"],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Yordis Prieto","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}],"database_specific":{"capec_ids":["CAPEC-130"],"cpe_ids":["cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-770"]},"details":"## Summary\n\nAllocation of Resources Without Limits or Throttling in ueberauth guardian allows denial of service via unbounded atom creation from attacker-controlled binary input.\n\nGuardian.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.\n\nString.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.\n\nThe default encoder is Guardian.Permissions.BitwiseEncoding, which is not affected.\n\nThis issue affects guardian: from 2.0.0 before 2.4.1.\n\n## Workaround\n\nSwitch the permission encoder to the default Guardian.Permissions.BitwiseEncoding or to Guardian.Permissions.TextEncoding, neither of which creates atoms. Alternatively, validate every permission value against the configured perm\\_set allowlist (rejecting unknown values) before passing it to encode/3.\n\n## Configuration\n\nOnly applications that opt into the non-default Guardian.Permissions.AtomEncoding encoder (via use Guardian.Permissions, encoding: Guardian.Permissions.AtomEncoding) and pass attacker-influenced permission scopes into its encode/3 entry point are exploitable. The default Guardian.Permissions.BitwiseEncoding encoder and the Guardian.Permissions.TextEncoding encoder do not create atoms and are not affected.","id":"EEF-CVE-2026-55733","modified":"2026-08-01T18:46:12.113Z","published":"2026-08-01T18:46:12.113Z","references":[{"type":"ADVISORY","url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-fjr5-7xrc-hmpj"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-55733.html"},{"type":"FIX","url":"https://github.com/ueberauth/guardian/commit/9cd268557846aa4c3ad53566c08f2c190ee5513f"},{"type":"PACKAGE","url":"https://hex.pm/packages/guardian"}],"related":[],"schema_version":"1.7.3","severity":[{"score":"CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H","type":"CVSS_V4"}],"summary":"Atom-table exhaustion denial of service in Guardian permissions AtomEncoding via unbounded atom creation","upstream":[]}