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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-53426?
1 open source package ship an affected version, including mdex.
| Package | 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-53426 being exploited?
There is no known exploitation of CVE-2026-53426 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-53426, GHSA-923r-7vf4-5vw8.