# CVE-2026-53426: Atom-table exhaustion denial-of-service via JSON parse_document in MDEx

> An attacker can crash the Erlang VM by sending crafted JSON to MDEx, exhausting the atom table and causing a denial of service.

- **Severity:** High 8.2 (`CVSS:4.0/AV:L/AC:L/AT:N/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:** 29 Jun 2026
- **Updated:** 30 Jun 2026
- **Also known as:** EEF-CVE-2026-53426, GHSA-923r-7vf4-5vw8

## What is CVE-2026-53426?

CVE-2026-53426 is a high-severity denial of service vulnerability in leandrocp mdex, published on 29 Jun 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 leandrocp MDEx allows Excessive Allocation.

MDEx.parse_document/2 accepts a {:json, json} source. In lib/mdex.ex, the private json_to_node/1 function passes the attacker-controlled node_type value to Module.concat/1, which calls String.to_atom/1 and interns a brand-new atom for every distinct value. Atoms are never garbage collected on the BEAM, so a crafted JSON document carrying a unique node_type at each (deeply nested) node mints one permanent atom per node.

A single document can intern hundreds of thousands of atoms, and a large enough document exhausts the default atom table (around 1,048,576 atoms) and aborts the entire Erlang VM, taking down every process on the node. Any application that passes untrusted input to the {:json, ...} source of MDEx.parse_document is exposed to an unauthenticated denial-of-service.

This issue affects mdex from 0.4.3 before 0.13.2.

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

## Which versions are affected by CVE-2026-53426?

1 open source package ship an affected version, including mdex.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mdex` | Hex | From 0.4.3 | 0.13.2 |

## How do I fix CVE-2026-53426?

Upgrade mdex to 0.13.2 or later.

## Is CVE-2026-53426 being exploited?

There is no known exploitation of CVE-2026-53426 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53426 and fix it if it is affected.

What it is: CVE-2026-53426 is a high-severity denial of service vulnerability in leandrocp mdex, published on 29 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-53426 in the wild and no public exploit code.

Affected packages and fixed versions:
- mdex (Hex): affected from 0.4.3; fixed in 0.13.2

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-2026-53426/ (Markdown: https://insights.sbomify.com/CVE-2026-53426/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53426
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53426
- OSV: https://osv.dev/vulnerability/CVE-2026-53426

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53426/
Summaries are generated and may contain mistakes; the official description above is the record.