{"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":"8d4efbfc352d30f5fcfc75a4d69a795b0e472724"}],"repo":"https://github.com/ueberauth/guardian","type":"GIT"}]}],"aliases":["GHSA-9qx2-v587-q3gg","CVE-2026-55734"],"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 vulnerability in ueberauth guardian (Guardian.Permissions module) allows a denial of service via BEAM atom-table exhaustion.\n\nThis vulnerability is associated with program file lib/guardian/permissions.ex and program routines 'Elixir.Guardian.Permissions':encode\\_permissions!/1, 'Elixir.Guardian.Permissions':encode\\_permissions\\_into\\_claims!/2, 'Elixir.Guardian.Permissions':do\\_encode\\_permissions!/2.\n\nThe Guardian.Permissions mixin installs a public encode\\_permissions!/1 function on every module that does use Guardian.Permissions. For each key of the supplied map, encode\\_permissions!/1 calls String.to\\_atom(to\\_string(k)) before any validation runs. The integer-value clause of do\\_encode\\_permissions!/2 then short-circuits straight to encoding without validating the key against the configured permission set, so a key with an integer value is interned as a fresh atom with no exception raised. Atoms are never garbage collected and the BEAM atom table is a fixed-size resource (default roughly 1,048,576 entries), so each unique attacker-chosen key permanently consumes one slot. An attacker who can influence a permission map that reaches encode\\_permissions!/1 (for example a permissions map read from a request body and passed into token issuance via encode\\_permissions\\_into\\_claims!/2) can mint an unbounded number of atoms and exhaust the atom table, crashing the entire BEAM node and every service running on it. The sibling decode\\_permissions/1 is not affected because it skips keys absent from the configured permission set.\n\nThis issue affects guardian: from 2.0.0 before 2.4.1.\n\n## Workaround\n\nBefore calling encode\\_permissions!/1 or encode\\_permissions\\_into\\_claims!/2, filter the permission map so that only keys belonging to the configured permission set are passed in, discarding any unknown keys. Avoid passing attacker-influenced permission maps into these functions.\n\n## Configuration\n\nThis vulnerability is only exploitable in applications that use Guardian.Permissions (via use Guardian.Permissions) and route attacker-influenced data into encode\\_permissions!/1 or encode\\_permissions\\_into\\_claims!/2, for example by reading a permissions map from a request body and passing it into token issuance.","id":"EEF-CVE-2026-55734","modified":"2026-08-01T18:46:24.291Z","published":"2026-08-01T18:46:24.291Z","references":[{"type":"ADVISORY","url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-9qx2-v587-q3gg"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-55734.html"},{"type":"FIX","url":"https://github.com/ueberauth/guardian/commit/8d4efbfc352d30f5fcfc75a4d69a795b0e472724"},{"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":"guardian atom exhaustion in Guardian.Permissions.encode_permissions!/1","upstream":[]}