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VulnerabilityPublished Updated

CVE-2026-55733: ueberauth guardian · Unthrottled Resource Allocation

Affects ueberauth guardianSource CVE Database V5

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Not known to be exploited · CVSS 6.9 Medium : upgrade to 2.4.1 when convenient.

Data as of 31 Oct 2026, 08:20 UTC

CVSS 4.0 base score
6.9Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 41% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.4.1, 9cd268557846aa4c3ad53566c08f2c190ee5513f
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

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 1 Aug 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade guardian to 2.4.1; guardian to 9cd268557846aa4c3ad53566c08f2c190ee5513f.

Affected software

ProductAffectedFixed in
ueberauthguardianAffected
  • >=2.0.0 <2.4.1
Fixed in
  • 2.4.1
ueberauthguardianAffected
  • ≥ b7a6128ca4d0ffb7f7df5219dd982304ff9d6802, < 9cd268557846aa4c3ad53566c08f2c190ee5513f
Fixed in
  • 9cd268557846aa4c3ad53566c08f2c190ee5513f
Hexguardianpkg:hex/guardianOther threatsAffected
  • >=2.0.0 <2.4.1
Fixed in
  • 2.4.1

CPE configurations (1)

  • cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

If you cannot patch yet, avoid using Guardian.Permissions.AtomEncoding for encoding permission scopes with untrusted input. Prefer the default Guardian.Permissions.BitwiseEncoding encoder or implement input validation and allow-listing to prevent 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. 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.

References

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