# CVE-2026-54894: Atom-table exhaustion denial of service in Guardian via unbounded atom creation from binary keys

> Attackers can crash the Elixir BEAM node by exhausting the atom table via unbounded atom creation from attacker-controlled input in Guardian.Plug.Keys.

- **Severity:** Medium 6.9 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Aug 2026
- **Updated:** 3 Aug 2026
- **Also known as:** EEF-CVE-2026-54894, GHSA-xqch-c77q-rgh5

## What is CVE-2026-54894?

CVE-2026-54894 is a medium-severity denial of service vulnerability in ueberauth guardian, published on 1 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Allocation of Resources Without Limits or Throttling in ueberauth guardian allows denial of service via unbounded atom creation from attacker-influenced binary input.

Guardian.Plug.Keys derives connection and session namespace keys by passing arbitrary binaries to String.to_atom/1. base_key/1 in lib/guardian/plug/keys.ex converts any binary into the atom :"guardian_<input>", and the derived helpers claims_key/1, resource_key/1, and token_key/1 create a second atom on top of that. key_from_other/1 likewise converts a regex-captured binary through String.to_atom/1. The public specs advertise String.t() as a valid argument, so passing a string is documented usage, and higher-level entry points such as Guardian.Plug.current_token(conn, key: key) thread the caller-supplied key straight into these functions.

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 routes attacker-influenced data (a tenant identifier, header, or other request input) into a Guardian key 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, taking down every application running on it.

This issue affects guardian: from 0.1.0 before 2.4.1.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-54894?

1 open source package ship an affected version, including guardian. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `guardian` | Hex | From 0.1.0 | 2.4.1 |

Products: Ueberauth Guardian.

## How do I fix CVE-2026-54894?

Upgrade guardian to 2.4.1 or later.

## Is CVE-2026-54894 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54894 exists.

## Other vulnerabilities in ueberauth guardian

- [CVE-2026-55735](https://insights.sbomify.com/CVE-2026-55735/): Guardian.revoke/3 acts on unverified token claims, allowing forged-token session revocation (high 8.2)
- [CVE-2026-55733](https://insights.sbomify.com/CVE-2026-55733/): Atom-table exhaustion denial of service in Guardian permissions AtomEncoding via unbounded atom creation (medium 6.9)
- [CVE-2026-55734](https://insights.sbomify.com/CVE-2026-55734/): guardian atom exhaustion in Guardian.Permissions.encode_permissions!/1 (medium 6.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54894 and fix it if it is affected.

What it is: CVE-2026-54894 is a medium-severity denial of service vulnerability in ueberauth guardian, published on 1 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54894 exists.

Affected packages and fixed versions:
- guardian (Hex): affected from 0.1.0; fixed in 2.4.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54894/ (Markdown: https://insights.sbomify.com/CVE-2026-54894/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54894
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54894
- OSV: https://osv.dev/vulnerability/CVE-2026-54894

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54894/
Summaries are generated and may contain mistakes; the official description above is the record.