{"id":"CVE-2026-55734","state":"PUBLISHED","title":"guardian atom exhaustion in Guardian.Permissions.encode_permissions!/1","description":"Allocation 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.","publishedAt":"2026-08-01T18:46:24.291Z","updatedAt":"2026-08-03T16:49:59.913Z","severity":{"score":6.9,"label":"Medium","version":"4.0","vector":"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","source":"EEF"},"assigner":"EEF","products":["ueberauth guardian"],"affected":[{"vendor":"ueberauth","product":"guardian","packageName":"guardian","packageURL":"pkg:hex/guardian","defaultStatus":"unaffected","versions":[{"version":"2.0.0","status":"affected","lessThan":"2.4.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Guardian.Permissions'"],"programFiles":["lib/guardian/permissions.ex"],"programRoutines":[{"name":"'Elixir.Guardian.Permissions':encode_permissions!/1"},{"name":"'Elixir.Guardian.Permissions':encode_permissions_into_claims!/2"},{"name":"'Elixir.Guardian.Permissions':do_encode_permissions!/2"}],"repo":"https://github.com/ueberauth/guardian"},{"vendor":"ueberauth","product":"guardian","packageName":"ueberauth/guardian","packageURL":"pkg:github/ueberauth/guardian","defaultStatus":"unaffected","versions":[{"version":"b7a6128ca4d0ffb7f7df5219dd982304ff9d6802","status":"affected","lessThan":"8d4efbfc352d30f5fcfc75a4d69a795b0e472724","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Guardian.Permissions'"],"programFiles":["lib/guardian/permissions.ex"],"programRoutines":[{"name":"'Elixir.Guardian.Permissions':encode_permissions!/1"},{"name":"'Elixir.Guardian.Permissions':encode_permissions_into_claims!/2"},{"name":"'Elixir.Guardian.Permissions':do_encode_permissions!/2"}],"repo":"https://github.com/ueberauth/guardian"}],"references":["https://github.com/ueberauth/guardian/security/advisories/GHSA-9qx2-v587-q3gg","https://cna.erlef.org/cves/CVE-2026-55734.html","https://osv.dev/vulnerability/EEF-CVE-2026-55734","https://github.com/ueberauth/guardian/commit/8d4efbfc352d30f5fcfc75a4d69a795b0e472724"],"weaknesses":["CWE-770"],"ingestedAt":"2026-10-29T20:12:24.861Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/55xxx/CVE-2026-55734.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-55734","state":"PUBLISHED","datePublished":"2026-08-01T18:46:24.291Z","dateUpdated":"2026-08-03T16:49:59.913Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-06-17T10:44:34.365Z"},"containers":{"cna":{"title":"guardian atom exhaustion in Guardian.Permissions.encode_permissions!/1","descriptions":[{"lang":"en","value":"Allocation 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."}],"affected":[{"vendor":"ueberauth","product":"guardian","packageName":"guardian","packageURL":"pkg:hex/guardian","defaultStatus":"unaffected","versions":[{"version":"2.0.0","status":"affected","lessThan":"2.4.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Guardian.Permissions'"],"programFiles":["lib/guardian/permissions.ex"],"programRoutines":[{"name":"'Elixir.Guardian.Permissions':encode_permissions!/1"},{"name":"'Elixir.Guardian.Permissions':encode_permissions_into_claims!/2"},{"name":"'Elixir.Guardian.Permissions':do_encode_permissions!/2"}],"repo":"https://github.com/ueberauth/guardian"},{"vendor":"ueberauth","product":"guardian","packageName":"ueberauth/guardian","packageURL":"pkg:github/ueberauth/guardian","defaultStatus":"unaffected","versions":[{"version":"b7a6128ca4d0ffb7f7df5219dd982304ff9d6802","status":"affected","lessThan":"8d4efbfc352d30f5fcfc75a4d69a795b0e472724","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Guardian.Permissions'"],"programFiles":["lib/guardian/permissions.ex"],"programRoutines":[{"name":"'Elixir.Guardian.Permissions':encode_permissions!/1"},{"name":"'Elixir.Guardian.Permissions':encode_permissions_into_claims!/2"},{"name":"'Elixir.Guardian.Permissions':do_encode_permissions!/2"}],"repo":"https://github.com/ueberauth/guardian"}],"references":[{"url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-9qx2-v587-q3gg","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-55734.html","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-55734","tags":["related"]},{"url":"https://github.com/ueberauth/guardian/commit/8d4efbfc352d30f5fcfc75a4d69a795b0e472724","tags":["patch"]}],"metrics":[{"cvssV4_0":{"attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"LOCAL","baseScore":6.9,"baseSeverity":"MEDIUM","privilegesRequired":"NONE","subAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"HIGH","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-770","description":"CWE-770 Allocation of Resources Without Limits or Throttling","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-08-01T18:46:24.291Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>This vulnerability is only exploitable in applications that use <tt>Guardian.Permissions</tt> (via <tt>use Guardian.Permissions</tt>) and route attacker-influenced data into <tt>encode_permissions!/1</tt> or <tt>encode_permissions_into_claims!/2</tt>, for example by reading a permissions map from a request body and passing it into token issuance.</p>"}],"value":"This 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."}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*","versionEndExcluding":"2.4.1","versionStartIncluding":"2.0.0","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"finder","value":"Peter Ullrich"},{"lang":"en","type":"remediation developer","value":"Yordis Prieto"},{"lang":"en","type":"analyst","value":"Jonatan Männchen / EEF"}],"impacts":[{"capecId":"CAPEC-130","descriptions":[{"lang":"en","value":"CAPEC-130 Excessive Allocation"}]}],"source":{"discovery":"EXTERNAL"},"workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>Before calling <tt>encode_permissions!/1</tt> or <tt>encode_permissions_into_claims!/2</tt>, 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.</p>"}],"value":"Before 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."}],"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-9qx2-v587-q3gg","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-03T16:49:36.457207Z","id":"CVE-2026-55734","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-03T16:49:59.913Z"}}]}}}