CVE-2026-55734 (GCVE-0-2026-55734)
Vulnerability from cvelistv5 – Published: 2026-08-01 18:46 – Updated: 2026-08-03 16:49
VLAI
EPSS
VEX
Title
guardian atom exhaustion in Guardian.Permissions.encode_permissions!/1
Summary
Allocation of Resources Without Limits or Throttling vulnerability in ueberauth guardian (Guardian.Permissions module) allows a denial of service via BEAM atom-table exhaustion.
This 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.
The 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.
This issue affects guardian: from 2.0.0 before 2.4.1.
Severity
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-03 16:49 UTC
CWE
- CWE-770 - Allocation of Resources Without Limits or Throttling
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/ueberauth/guardian/security/ad… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-55734.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-55734 | related |
| https://github.com/ueberauth/guardian/commit/8d4e… | patch |
Impacted products
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"vulnrichment": {
"containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-55734\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"poc\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-03T16:49:36.457207Z\"}}}], \"references\": [{\"url\": \"https://github.com/ueberauth/guardian/security/advisories/GHSA-9qx2-v587-q3gg\", \"tags\": [\"exploit\"]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-03T16:49:54.930Z\"}}], \"cna\": {\"title\": \"guardian atom exhaustion in Guardian.Permissions.encode_permissions!/1\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Peter Ullrich\"}, {\"lang\": \"en\", \"type\": \"remediation developer\", \"value\": \"Yordis Prieto\"}, {\"lang\": \"en\", \"type\": \"analyst\", \"value\": \"Jonatan M\\u00e4nnchen / EEF\"}], \"impacts\": [{\"capecId\": \"CAPEC-130\", \"descriptions\": [{\"lang\": \"en\", \"value\": \"CAPEC-130 Excessive Allocation\"}]}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"version\": \"4.0\", \"baseScore\": 6.9, \"attackVector\": \"LOCAL\", \"baseSeverity\": \"MEDIUM\", \"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\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"attackRequirements\": \"PRESENT\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"NONE\", \"subAvailabilityImpact\": \"HIGH\", \"vulnAvailabilityImpact\": \"HIGH\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"NONE\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/ueberauth/guardian\", \"vendor\": \"ueberauth\", \"modules\": [\"\u0027Elixir.Guardian.Permissions\u0027\"], \"product\": \"guardian\", \"versions\": [{\"status\": \"affected\", \"version\": \"2.0.0\", \"lessThan\": \"2.4.1\", \"versionType\": \"semver\"}], \"packageURL\": \"pkg:hex/guardian\", \"packageName\": \"guardian\", \"programFiles\": [\"lib/guardian/permissions.ex\"], \"collectionURL\": \"https://repo.hex.pm\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"\u0027Elixir.Guardian.Permissions\u0027:encode_permissions!/1\"}, {\"name\": \"\u0027Elixir.Guardian.Permissions\u0027:encode_permissions_into_claims!/2\"}, {\"name\": \"\u0027Elixir.Guardian.Permissions\u0027:do_encode_permissions!/2\"}]}, {\"cpes\": [\"cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/ueberauth/guardian\", \"vendor\": \"ueberauth\", \"modules\": [\"\u0027Elixir.Guardian.Permissions\u0027\"], \"product\": \"guardian\", \"versions\": [{\"status\": \"affected\", \"version\": \"b7a6128ca4d0ffb7f7df5219dd982304ff9d6802\", \"lessThan\": \"8d4efbfc352d30f5fcfc75a4d69a795b0e472724\", \"versionType\": \"git\"}], \"packageURL\": \"pkg:github/ueberauth/guardian\", \"packageName\": \"ueberauth/guardian\", \"programFiles\": [\"lib/guardian/permissions.ex\"], \"collectionURL\": \"https://github.com\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"\u0027Elixir.Guardian.Permissions\u0027:encode_permissions!/1\"}, {\"name\": \"\u0027Elixir.Guardian.Permissions\u0027:encode_permissions_into_claims!/2\"}, {\"name\": \"\u0027Elixir.Guardian.Permissions\u0027:do_encode_permissions!/2\"}]}], \"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\"]}], \"workarounds\": [{\"lang\": \"en\", \"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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eBefore calling \u003ctt\u003eencode_permissions!/1\u003c/tt\u003e or \u003ctt\u003eencode_permissions_into_claims!/2\u003c/tt\u003e, 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.\u003c/p\u003e\", \"base64\": false}]}], \"x_generator\": {\"engine\": \"cvelib 1.8.0\"}, \"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 \u0027Elixir.Guardian.Permissions\u0027:encode_permissions!/1, \u0027Elixir.Guardian.Permissions\u0027:encode_permissions_into_claims!/2, \u0027Elixir.Guardian.Permissions\u0027: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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eAllocation of Resources Without Limits or Throttling vulnerability in ueberauth guardian (\u003ctt\u003eGuardian.Permissions\u003c/tt\u003e module) allows a denial of service via BEAM atom-table exhaustion.\u003c/p\u003e\u003cp\u003eThis vulnerability is associated with program file \u003ctt\u003elib/guardian/permissions.ex\u003c/tt\u003e and program routines \u003ctt\u003e\u0027Elixir.Guardian.Permissions\u0027:encode_permissions!/1\u003c/tt\u003e, \u003ctt\u003e\u0027Elixir.Guardian.Permissions\u0027:encode_permissions_into_claims!/2\u003c/tt\u003e, \u003ctt\u003e\u0027Elixir.Guardian.Permissions\u0027:do_encode_permissions!/2\u003c/tt\u003e.\u003c/p\u003e\u003cp\u003eThe \u003ctt\u003eGuardian.Permissions\u003c/tt\u003e mixin installs a public \u003ctt\u003eencode_permissions!/1\u003c/tt\u003e function on every module that does \u003ctt\u003euse Guardian.Permissions\u003c/tt\u003e. For each key of the supplied map, \u003ctt\u003eencode_permissions!/1\u003c/tt\u003e calls \u003ctt\u003eString.to_atom(to_string(k))\u003c/tt\u003e before any validation runs. The integer-value clause of \u003ctt\u003edo_encode_permissions!/2\u003c/tt\u003e 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 \u003ctt\u003eencode_permissions!/1\u003c/tt\u003e (for example a permissions map read from a request body and passed into token issuance via \u003ctt\u003eencode_permissions_into_claims!/2\u003c/tt\u003e) 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 \u003ctt\u003edecode_permissions/1\u003c/tt\u003e is not affected because it skips keys absent from the configured permission set.\u003c/p\u003e\u003cp\u003eThis issue affects guardian: from 2.0.0 before 2.4.1.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-770\", \"description\": \"CWE-770 Allocation of Resources Without Limits or Throttling\"}]}], \"configurations\": [{\"lang\": \"en\", \"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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eThis vulnerability is only exploitable in applications that use \u003ctt\u003eGuardian.Permissions\u003c/tt\u003e (via \u003ctt\u003euse Guardian.Permissions\u003c/tt\u003e) and route attacker-influenced data into \u003ctt\u003eencode_permissions!/1\u003c/tt\u003e or \u003ctt\u003eencode_permissions_into_claims!/2\u003c/tt\u003e, for example by reading a permissions map from a request body and passing it into token issuance.\u003c/p\u003e\", \"base64\": false}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"2.4.1\", \"versionStartIncluding\": \"2.0.0\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-08-01T18:46:24.291Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-55734\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-03T16:49:59.913Z\", \"dateReserved\": \"2026-06-17T10:44:34.365Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-08-01T18:46:24.291Z\", \"assignerShortName\": \"EEF\"}",
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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