{"id":"CVE-2026-55733","summary":"Atom-table exhaustion denial of service in Guardian permissions AtomEncoding via unbounded atom creation","details":"Allocation 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.","aliases":["EEF-CVE-2026-55733","GHSA-fjr5-7xrc-hmpj"],"modified":"2026-08-03T03:45:40.623034211Z","published":"2026-08-01T18:46:12.113Z","database_specific":{"cwe_ids":["CWE-770"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55733.json","unresolved_ranges":[{"source":"AFFECTED_FIELD","extracted_events":[{"introduced":"b7a6128ca4d0ffb7f7df5219dd982304ff9d6802"},{"fixed":"9cd268557846aa4c3ad53566c08f2c190ee5513f"}]}],"cna_assigner":"EEF"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-55733.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-55733"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55733.json"},{"type":"ADVISORY","url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-fjr5-7xrc-hmpj"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55733"},{"type":"FIX","url":"https://github.com/ueberauth/guardian/commit/9cd268557846aa4c3ad53566c08f2c190ee5513f"},{"type":"PACKAGE","url":"https://github.com/ueberauth/guardian"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ueberauth/guardian","events":[{"introduced":"576997d3701306ccfa40b42e18b1bec5a6ac98a7"},{"fixed":"e6017b492b8ef55e24fd08dea45ce11780d7b4f7"},{"fixed":"9cd268557846aa4c3ad53566c08f2c190ee5513f"}],"database_specific":{"extracted_events":[{"introduced":"2.0.0"},{"fixed":"2.4.1"}],"source":["DESCRIPTION","REFERENCES"]}}],"versions":["v2.4.0","v2.3.2","v2.3.1","v2.3.0","v2.2.4","v2.2.3","v2.2.2","v2.2.1","v2.1.2","v2.1.1","2.1.0","v2.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55733.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","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"}]}