# CVE-2026-55734: guardian atom exhaustion in Guardian.Permissions.encode_permissions!/1 > An attacker can crash the BEAM node by exhausting the atom table via unvalidated keys in permission maps, affecting Elixir Guardian library users. - **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-2026-55734, GHSA-9qx2-v587-q3gg ## What is CVE-2026-55734? CVE-2026-55734 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 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. Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling) ## Which versions are affected by CVE-2026-55734? 1 open source package ship an affected version, including guardian. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `guardian` | Hex | From 2.0.0 | 2.4.1 | Products: Ueberauth Guardian. ## How do I fix CVE-2026-55734? Upgrade guardian to 2.4.1 or later. ## Is CVE-2026-55734 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55734 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-2026-54894](https://insights.sbomify.com/CVE-2026-54894/): Atom-table exhaustion denial of service in Guardian via unbounded atom creation from binary keys (medium 6.9) - [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) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-55734 and fix it if it is affected. What it is: CVE-2026-55734 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-2026-55734 exists. Affected packages and fixed versions: - guardian (Hex): affected from 2.0.0; 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-2026-55734/ (Markdown: https://insights.sbomify.com/CVE-2026-55734/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55734 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55734 - OSV: https://osv.dev/vulnerability/CVE-2026-55734 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-55734/ Summaries are generated and may contain mistakes; the official description above is the record.