Is CVE-2026-53426 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-53426 being exploited in the wild.

How severe is CVE-2026-53426?

Informational severity, with a CVSS score of 8.2, published 29 June 2026.

Which products and versions are affected?

leandrocp mdex 0.4.3 to 0.13.1.

Is there a fix for CVE-2026-53426?

A patch was published on 2026-06-29. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-53426 attacked?

It is attacked with local access, in a software library.

Am I affected by CVE-2026-53426?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-53426: leandrocp MDEx atom-table exhaustion in parse_document

CVE-2026-53426 · Severity: info · CVSS 8.2 · Published 2026-06-29

A vulnerability in the MDEx Markdown library for Elixir can allow an attacker to crash the entire application server. By providing a specially crafted JSON document, an attacker can exhaust the system's memory for internal identifiers (atoms), which are never cleared. This results in a complete denial-of-service, forcing the entire Erlang virtual machine to shut down and stopping all running processes.

Quick answers

Is CVE-2026-53426 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-53426 being exploited in the wild.
How severe is CVE-2026-53426?: Informational severity, with a CVSS score of 8.2, published 29 June 2026.
Which products and versions are affected?: leandrocp mdex 0.4.3 to 0.13.1.
Is there a fix for CVE-2026-53426?: A patch was published on 2026-06-29. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-53426 attacked?: It is attacked with local access, in a software library.
Am I affected by CVE-2026-53426?: Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The MDEx.parse_document/2 function, when processing a {:json, json} source, utilizes a private function json_to_node/1 that passes attacker-controlled 'node_type' values to Module.concat/1. This internally calls String.to_atom/1, interning a new atom for every unique value provided. Because atoms in the Erlang BEAM VM are not garbage collected, a deeply nested JSON document with unique node types can exhaust the default atom table limit (approximately 1 million). Once this limit is reached, the entire Erlang VM aborts. This is an unauthenticated denial-of-service reachable if the application processes untrusted JSON input via MDEx.

Affected products

leandrocp mdex 0.4.3 to 0.13.1

Timeline

2026-06-29: advisory
2026-06-29: disclosed
2026-06-29: patched

References

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