{"id":"CVE-2026-55733","state":"PUBLISHED","title":"Atom-table exhaustion denial of service in Guardian permissions AtomEncoding via unbounded atom creation","description":"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.","publishedAt":"2026-08-01T18:46:12.113Z","updatedAt":"2026-08-03T16:50:53.942Z","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.AtomEncoding'"],"programFiles":["lib/guardian/permissions/atom_encoding.ex"],"programRoutines":[{"name":"'Elixir.Guardian.Permissions.AtomEncoding':encode/3"},{"name":"'Elixir.Guardian.Permissions.AtomEncoding':encode_value/3"}],"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":"9cd268557846aa4c3ad53566c08f2c190ee5513f","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Guardian.Permissions.AtomEncoding'"],"programFiles":["lib/guardian/permissions/atom_encoding.ex"],"programRoutines":[{"name":"'Elixir.Guardian.Permissions.AtomEncoding':encode/3"},{"name":"'Elixir.Guardian.Permissions.AtomEncoding':encode_value/3"}],"repo":"https://github.com/ueberauth/guardian"}],"references":["https://github.com/ueberauth/guardian/security/advisories/GHSA-fjr5-7xrc-hmpj","https://cna.erlef.org/cves/CVE-2026-55733.html","https://osv.dev/vulnerability/EEF-CVE-2026-55733","https://github.com/ueberauth/guardian/commit/9cd268557846aa4c3ad53566c08f2c190ee5513f"],"weaknesses":["CWE-770"],"ingestedAt":"2026-10-29T20:12:24.861Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/55xxx/CVE-2026-55733.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-55733","state":"PUBLISHED","datePublished":"2026-08-01T18:46:12.113Z","dateUpdated":"2026-08-03T16:50:53.942Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-06-17T10:44:34.365Z"},"containers":{"cna":{"title":"Atom-table exhaustion denial of service in Guardian permissions AtomEncoding via unbounded atom creation","descriptions":[{"lang":"en","value":"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."}],"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.AtomEncoding'"],"programFiles":["lib/guardian/permissions/atom_encoding.ex"],"programRoutines":[{"name":"'Elixir.Guardian.Permissions.AtomEncoding':encode/3"},{"name":"'Elixir.Guardian.Permissions.AtomEncoding':encode_value/3"}],"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":"9cd268557846aa4c3ad53566c08f2c190ee5513f","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Guardian.Permissions.AtomEncoding'"],"programFiles":["lib/guardian/permissions/atom_encoding.ex"],"programRoutines":[{"name":"'Elixir.Guardian.Permissions.AtomEncoding':encode/3"},{"name":"'Elixir.Guardian.Permissions.AtomEncoding':encode_value/3"}],"repo":"https://github.com/ueberauth/guardian"}],"references":[{"url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-fjr5-7xrc-hmpj","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-55733.html","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-55733","tags":["related"]},{"url":"https://github.com/ueberauth/guardian/commit/9cd268557846aa4c3ad53566c08f2c190ee5513f","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":"2026-08-01T18:46:12.113Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>Only applications that opt into the non-default <tt>Guardian.Permissions.AtomEncoding</tt> encoder (via <tt>use Guardian.Permissions, encoding: Guardian.Permissions.AtomEncoding</tt>) and pass attacker-influenced permission scopes into its <tt>encode/3</tt> entry point are exploitable. The default <tt>Guardian.Permissions.BitwiseEncoding</tt> encoder and the <tt>Guardian.Permissions.TextEncoding</tt> encoder do not create atoms and are not affected.</p>"}],"value":"Only 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."}],"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>Switch the permission encoder to the default <tt>Guardian.Permissions.BitwiseEncoding</tt> or to <tt>Guardian.Permissions.TextEncoding</tt>, neither of which creates atoms. Alternatively, validate every permission value against the configured <tt>perm_set</tt> allowlist (rejecting unknown values) before passing it to <tt>encode/3</tt>.</p>"}],"value":"Switch 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."}],"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-fjr5-7xrc-hmpj","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-03T16:50:27.758398Z","id":"CVE-2026-55733","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":"2026-08-03T16:50:53.942Z"}}]}}}