CVE-2026-55733
Allocation of Resources Without Limits or Throttling in ueberauth guardian allows denial of service via unbounded atom creation from attacker-controlled binary input.
Does this matter?
Lower severity and a low EPSS score (0.32%). Track it; it rarely justifies an emergency change on its own.
Description
Allocation of Resources Without Limits or Throttling in ueberauth guardian allows denial of service via unbounded atom creation from attacker-controlled binary input. Guardian.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. String.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. The default encoder is Guardian.Permissions.BitwiseEncoding, which is not affected. This issue affects guardian: from 2.0.0 before 2.4.1.
- CVSS 4.0
- 6.9 MEDIUMCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.32% probability · 25th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-770
- Affected
- ueberauth/guardian
- Source
- 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
References
- https://cna.erlef.org/cves/CVE-2026-55733.htmlThird Party Advisory
- https://github.com/ueberauth/guardian/commit/9cd268557846aa4c3ad53566c08f2c190ee5513fPatch
- https://github.com/ueberauth/guardian/security/advisories/GHSA-fjr5-7xrc-hmpjExploit, Patch, Vendor Advisory
- https://osv.dev/vulnerability/EEF-CVE-2026-55733Third Party Advisory
- https://github.com/ueberauth/guardian/security/advisories/GHSA-fjr5-7xrc-hmpjExploit, Patch, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.