{"id":"CVE-2026-55733","aliases":["EEF-CVE-2026-55733","GHSA-fjr5-7xrc-hmpj"],"url":"https://o3.security/vulnerability/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.","published":"2026-08-01T18:46:12.113Z","modified":"2026-08-12T03:51:46.323961860Z","cvss":null,"epss":{"score":0.00271,"percentile":0.19314,"asOf":"2026-08-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[],"fix":{"url":"https://github.com/ueberauth/guardian/commit/9cd268557846aa4c3ad53566c08f2c190ee5513f","label":"ueberauth/guardian@9cd2685"},"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:46.323961860Z"}}